Bootloader unlock ?????? - Nokia 6.1 Plus (X6) Questions & Answers

Why we can't access bootloader option in developer option in recent updates.
Why such thing is done by Nokia ...
Is it possible for our device to install twrp gsi and custom ROM as easily as some other devices....

Answer
https://www.xda-developers.com/august-security-update-on-nokia-phones-blocks-the-only-bootloader-unlock-method/
You need to get back to stock firmware prior to August update ( Out of the box OS, Oreo would be best ).
Only way after Pie update is go to a Nokia care center - and rollback.

Related

What does OTA package checks for ?

Hi guys,
It may be a silly Question for this Device , let me tell you my device specs :
Device : G4 Plus XT1643(India)
Rom : Stock (Soak NPJ75.25.2)
NON-Root and Locked Bootloader
What does the OTA.zip checks for ?
Boot image version (may b bootloader version) or recovery version ?
If its all about bootloader, then it needs to b unlocked voiding warranty.
But If its about Recovery..........Changing the Recovery to older version might help updating from Old Soak to New Official Build.
So, Did any one try flashing an older recovery thru fastboot on locked bootloader ? or Can we if its possible ?
ex: Replacing 7.0 recovery with last 6.0 build recovery. I do this for my ZenFone 5 just to avoid updating from very old builds.
Is this possible on G4 Plus ? without warranty Void issues....if possible.
p.s: NPJ93-11 gives Status 7 error on NPJ.75-2.
I tried to flash old recovery but it fails due to higher bootloader version.
Same question. Experts please advise and find a solution to get official update without unlocking the bootloader.
praveenbda said:
Same question. Experts please advise and find a solution to get official update without unlocking the bootloader.
Click to expand...
Click to collapse
You don't need to unlock your bootloader to get an OTA. Its only to let you mess with your recovery and enable flashing henceforth.
However, you'll need to unlock your bootloader to flash/boot a custom recovery and subsequently flash a ROM.
But if you want an OTA, your system (including bootloader, recovery, system, etc) needs to be untouched.
If you've already upgraded to a soak test, remember - you would've overwritten your MM bootloader and recovery with an N version one (from the Soak you sideloaded)
Again, all major official updates (except small incremental one like patches maybe) look for a previous version of the OS (in our case - Stock MM)
And yes, as long you're on MM and not upgraded to N soak ever, once you unlock your BL, you can relock it using methods stated in the guide thread. Just that it voids your warranty (as the request code is generated by Lenovo/Moto, essentially letting you unlock) But if you've flashed the N Soak - you can't downgrade your bootloader just yet ( you'll get a Preflash Validation error)
Because a system update looks the stock, untouched firmware (Stock MM)
That's why you won't be able to sideload the Official N update if you're already on a soak test update - because it doesn't have the MM bootloader and recovery etc files it's looking for.
Sent from my Moto G4 Plus using Tapatalk

Custom ROMs and future updates. What do I have to bear in mind?

So, we all know Motorola will eventually (aka never) release Oreo for the G5 Plus.
I am way too anxious so I am going to flash a Custom ROM until they deliver it. However I am quite afraid about something.
I plan to use Lineage 15.1 until Oreo comes out for the G5 Plus. However, I am kind of afraid that I may screw things up when the OTA comes out.
I have recently hard bricked my Moto G 2014 because of OTAs and Bootloader.
So, Oreo releases...
Will it be fine to install the OTA (through normal System Update check) having the latest Stock ROM Firmware for my region installed? (I would erase Lineage 15 and use fastboot to flash Stock again)
Or will I instead need to wait for someone to post the system images and flash it through fastboot instead? (I assume I would need to install the OTA through normal methods because of bootloader changes but still...)
I just don't want this: https://forum.xda-developers.com/g5-plus/help/moto-g5-plus-hard-bricked-t3694119
To happen.
You won't get system updates when you are on a custom ROM like Lineage OS or any other custom ROM. The only system updates you might get are ROM updates if the ROM maintainer has that feature built in.
If official Oreo comes out and you are on the correct stock firmware for your model and region, everything should work fine.
Before flashing custom roms you should backup your efs partition using twrp else you could lose your imei(recoverable) / volte(not recoverable till now) when flashing fastboot firmwire.
You need to flash fastboot firmwire to receive oreo ota.
If you want to avoid hard bricking, then you must flash the same stock ROM or newer onto your device when you revert back to stock firmware.
I imagine your Moto G 2014 got bricked when you took an OTA update? That could have occurred if firmware older than what was present on your device was flashed (bootloaders cannot be downgraded), and like in that thread you linked, attempting to use OTA updates would corrupt your newer bootloader with the older OTA patches, leading to a hard brick.
As mentioned above, if you revert to the correct build for your region and matching your current build at least, you should be okay to receive OTA updates (should also include up to Oreo). Alternatively, you could wait for the Oreo fastboot ROM to be safe, or the Oreo TWRP flashable for a near stock ROM experience (since TWRP flashables shouldn't care about your bootloader or GPT partitions, do it'd be difficult to brick your device. However, TWRP flashable stock ROMs aren't OTA compatible).
Before you unlock your bootloader and flash TWRP/custom ROMs, make a note of your current build version and see if you can find a stock ROM leaked of that build, so you can be sure that you're reverting to the right build for your device.
Just do not flash older stock Motorola firmware to your device or if you do, do not use OTA updates.
Yeah, I did some research and now I understand what happened. Thanks for the comments.

Unlocked bootloader and OTA updates

Will i recive OTA update if i unlock the bootloader?
Androidtroll said:
Will i recive OTA update if i unlock the bootloader?
Click to expand...
Click to collapse
Yes. Just unlocking the bootloader still allows everything to work normally, though you can't install otas if you mounted or modified /system and /oem partitions, or have twrp recovery.
Otherwise your phone should still function as if it weren't unlocked.
In addition to the above reply - if you do modify your system and want to flash back to stock firmware, please check if you can download the correct firmware for your device. I see from your history you have a retEU device, so the latest series of firmwares would be the NPNS25.137-93 series (with NPNS25.137-93-10 being the April 2018 security patch). I'd suggest checking to see if there is a stock ROM matching your current build before you unlock the bootloader (either at https://mirrors.lolinet.com/firmware/moto/potter/official/RETAIL/ or https://firmware.center/firmware/Motorola/Moto G5 Plus/Stock/ or https://androidfilehost.com/?a=show&w=files&flid=171014 ) though it seems the latest firmware that's been leaked is NPNS25.137-93-4 (the Jan 2018 security patch build). Just as a headsup, firmware.center has a cryptominer that could keep your CPU at 100 % if you have their page open.
If you download and flash the NPNS25.137-92-10 firmware, which is the April 2018 security patch for Brazil/India devices, you may be able to re-lock your bootloader and get back to full stock, but you may not be able to receive OTA updates (as the NPNS25.137-92 series of updates do not appear to be deployed to the retEU channel), so be careful which firmware you flash.
You can still unlock your bootloader without having the latest firmware to hand, but until the firmware matching your stock firmware before you unlocked or newer is available, you may not be able to re-lock your device. You may be able to flash older stock firmware for EU devices, but please do not use OTA updates if you flash older stock firmware, else you may hard brick your device.
Good luck whichever way you decide.
bazinga137 said:
Yes. Just unlocking the bootloader still allows everything to work normally, though you can't install otas if you mounted or modified /system and /oem partitions, or have twrp recovery.
Otherwise, your phone should still function as if it weren't unlocked.
Click to expand...
Click to collapse
Yes the Same thing Happened
I had TWRP recovery and I installed the Security Patch
my Phone Stuck at TWRP
but it has One solution
First, take the data backup of all in twrp at your sd card
now install any custom Rom
Reboot your device and check the rom is working or not
do reboot and go back to your Twrp and Restore the backup
I tested it and It worked perfectly
echo92 said:
In addition to the above reply - if you do modify your system and want to flash back to stock firmware, please check if you can download the correct firmware for your device. I see from your history you have a retEU device, so the latest series of firmwares would be the NPNS25.137-93 series (with NPNS25.137-93-10 being the April 2018 security patch). I'd suggest checking to see if there is a stock ROM matching your current build before you unlock the bootloader (either at https://mirrors.lolinet.com/firmware/moto/potter/official/RETAIL/ or https://firmware.center/firmware/Motorola/Moto G5 Plus/Stock/ or https://androidfilehost.com/?a=show&w=files&flid=171014 ) though it seems the latest firmware that's been leaked is NPNS25.137-93-4 (the Jan 2018 security patch build). Just as a headsup, firmware.center has a cryptominer that could keep your CPU at 100 % if you have their page open.
If you download and flash the NPNS25.137-92-10 firmware, which is the April 2018 security patch for Brazil/India devices, you may be able to re-lock your bootloader and get back to full stock, but you may not be able to receive OTA updates (as the NPNS25.137-92 series of updates do not appear to be deployed to the retEU channel), so be careful which firmware you flash.
You can still unlock your bootloader without having the latest firmware to hand, but until the firmware matching your stock firmware before you unlocked or newer is available, you may not be able to re-lock your device. You may be able to flash older stock firmware for EU devices, but please do not use OTA updates if you flash older stock firmware, else you may hard brick your device.
Good luck whichever way you decide.
Click to expand...
Click to collapse
I would unlock the bootloader just to try to fix the camera (then edit the system files), not for flash twrp / custom rom
Androidtroll said:
I would unlock the bootloader just to try to fix the camera (then edit the system files), not for flash twrp / custom rom
Click to expand...
Click to collapse
Just unlocking the BL wouldn't be enough to edit system files. You'll need root privileges to do so and for that you will have to flash/boot TWRP to install a root app like magisk.
So all the useful information @echo92 posted above is significant for you.
Sent from my Moto G5 Plus using XDA Labs
Is there a way to take TWRP off or disable to still grab the security patches? Or is clean install/backup (like Rutambh mentioned) the only option? The reason I ask I needed TWRP to install camera mod, so it would be nice to still get those OTA's. I tried to just fastboot boot TWRP but it would just hang at it's logo. Flash was only option.
Frawgg said:
Is there a way to take TWRP off or disable to still grab the security patches? Or is clean install/backup (like Rutambh mentioned) the only option? The reason I ask I needed TWRP to install camera mod, so it would be nice to still get those OTA's. I tried to just fastboot boot TWRP but it would just hang at it's logo. Flash was only option.
Click to expand...
Click to collapse
If anything in /system or /oem is tampered like installing a camera mod (or just mounting system r/w) the only way to receive future OTA updates is flashing your current ROM incl. stock recovery via fastboot.
Sent from my Moto G5 Plus using XDA Labs

Help. phone dead

Hey. my phone was bootlooped and i recover to stock rom marshmallow 6.0. then came update 6.0.1 it was ok i installed it. after that came Nougat 7.1 update and in installation time phone won't boot. bootloader was unlocked. computer can not see phone, it says usb device not recognized. phone is moto g4 xt1622 dual sim
is there any way to survive? motherboard is dead? thanks. i can not know what to do i am so sorry i feel so bad
just there is white light phone is charging, but no switch on and no bootloader menu. nothing happens
gioyocho said:
Hey. my phone was bootlooped and i recover to stock rom marshmallow 6.0. then came update 6.0.1 it was ok i installed it. after that came Nougat 7.1 update and in installation time phone won't boot. bootloader was unlocked. computer can not see phone, it says usb device not recognized. phone is moto g4 xt1622 dual sim
is there any way to survive? motherboard is dead? thanks. i can not know what to do i am so sorry i feel so bad
just there is white light phone is charging, but no switch on and no bootloader menu. nothing happens
Click to expand...
Click to collapse
Looks like you downgraded your bootloader and then take ota = hardbrick. Have you tried that guide and read the discussion of others? https://forum.xda-developers.com/moto-g4-plus/how-to/moto-g4-plus-hardbrick-solved-guide-t3657761
strongst said:
Looks like you downgraded your bootloader and then take ota = hardbrick. Have you tried that guide and read the discussion of others? https://forum.xda-developers.com/moto-g4-plus/how-to/moto-g4-plus-hardbrick-solved-guide-t3657761
Click to expand...
Click to collapse
Thanks for reply! i used your link for stock rom marshmallow. but now computer can not see phone, it says not recognized. i can not get access to fastboot menu. i am going to take it to programmer, but i have no hope. so sad
gioyocho said:
Thanks for reply! i used your link for stock rom marshmallow. but now computer can not see phone, it says not recognized. i can not get access to fastboot menu. i am going to take it to programmer, but i have no hope. so sad
Click to expand...
Click to collapse
What do you see in Device Manager when your device is connected, do you see Qualcomm HS-USB 9008 or similar listed? Do you have the Motorola drivers installed on your computer, and, if you have Windows 8.1 or 10, do you have driver signature enforcement disabled? https://www.howtogeek.com/167723/ho...8.1-so-that-you-can-install-unsigned-drivers/
I'm confused that you used the link provided by strongst to flash a MM firmware though, from what I recall reading of your post it sounded like you soft bricked but somehow managed to flash a MM firmware. However, as strongst pointed out, if you'd downgraded your device when you flashed MM, taking the OTA update would have corrupted your bootloader, leaving you with the hard brick and no fastboot mode.
EDIT - looking through your previous posts, it looked like you had formally updated to stock Nougat, then downgraded to the stock MM firmware (but still had a Nougat bootloader - you cannot generally downgrade bootloaders), then using an old Nougat OTA corrupted your bootloader. Ouch... What firmware did you download?
I'd try to install the Motorola drivers to your computer https://support.motorola.com/us/en/drivers , disable driver signature enforcement if you can and then try the blankflash from that guide. If the blankflash can communicate with your device, then it may be able to flash a basic bootloader and give you fastboot. Ensure you use your original Motorola cable or a good quality USB data cable and that the physical connection to your device is good.
I am also faced same issue ,even Motorola service centre guys won't helped me. But I did it with patience ,I sure your problem will be with Qualcomm usb driver ,so install it correctly .
echo92 said:
What do you see in Device Manager when your device is connected, do you see Qualcomm HS-USB 9008 or similar listed? Do you have the Motorola drivers installed on your computer, and, if you have Windows 8.1 or 10, do you have driver signature enforcement disabled? https://www.howtogeek.com/167723/ho...8.1-so-that-you-can-install-unsigned-drivers/
I'm confused that you used the link provided by strongst to flash a MM firmware though, from what I recall reading of your post it sounded like you soft bricked but somehow managed to flash a MM firmware. However, as strongst pointed out, if you'd downgraded your device when you flashed MM, taking the OTA update would have corrupted your bootloader, leaving you with the hard brick and no fastboot mode.
EDIT - looking through your previous posts, it looked like you had formally updated to stock Nougat, then downgraded to the stock MM firmware (but still had a Nougat bootloader - you cannot generally downgrade bootloaders), then using an old Nougat OTA corrupted your bootloader. Ouch... What firmware did you download?
I'd try to install the Motorola drivers to your computer https://support.motorola.com/us/en/drivers , disable driver signature enforcement if you can and then try the blankflash from that guide. If the blankflash can communicate with your device, then it may be able to flash a basic bootloader and give you fastboot. Ensure you use your original Motorola cable or a good quality USB data cable and that the physical connection to your device is good.
Click to expand...
Click to collapse
Thanks for reply!
i had installed many drivers. even qualcomm and motorola, but situation is such. see file attachment. looks like my phone is in coma. i have windows 10. i will say long story short
1. i had android 8.1.0 RR, it was heating and i changed to RR 7.1.2. it worked good
2. it was also heating and i decides to change kernel and phone stop on RR logo, it was rounding but phone won't working. i had no backup or rom files
3. then i installed stock rom 6.0 marshmallow from fastboot with cmd, i downloded it from motorola's official site. i had 6.0 and bootloader unlocked. than came 6.0.1 ota and i updated it was ok. than came also ota update Nougat and installation process phone won't boot
echo92 said:
What do you see in Device Manager when your device is connected, do you see Qualcomm HS-USB 9008 or similar listed? Do you have the Motorola drivers installed on your computer, and, if you have Windows 8.1 or 10, do you have driver signature enforcement disabled? https://www.howtogeek.com/167723/ho...8.1-so-that-you-can-install-unsigned-drivers/
I'm confused that you used the link provided by strongst to flash a MM firmware though, from what I recall reading of your post it sounded like you soft bricked but somehow managed to flash a MM firmware. However, as strongst pointed out, if you'd downgraded your device when you flashed MM, taking the OTA update would have corrupted your bootloader, leaving you with the hard brick and no fastboot mode.
EDIT - looking through your previous posts, it looked like you had formally updated to stock Nougat, then downgraded to the stock MM firmware (but still had a Nougat bootloader - you cannot generally downgrade bootloaders), then using an old Nougat OTA corrupted your bootloader. Ouch... What firmware did you download?
I'd try to install the Motorola drivers to your computer https://support.motorola.com/us/en/drivers , disable driver signature enforcement if you can and then try the blankflash from that guide. If the blankflash can communicate with your device, then it may be able to flash a basic bootloader and give you fastboot. Ensure you use your original Motorola cable or a good quality USB data cable and that the physical connection to your device is good.
Click to expand...
Click to collapse
now i changed something, disabled test mode windows and it says some qualcomm device in device manager port. what i can do now?
Omg people i survived it again. you make me day i am so happy. just there is december security patch 2016 but i feel so great. the problem was next: when i installed many drivers and applications, windows came to test mode (it was written right and down side of screen), then i go to youtube and did everything exactly run as administrator and run words, then i restarted computer and it saw my qualcomm driver 9008 or something, i used blankfish file for install bootloader and downloaded 7.0 rom for 1 april security patches. i swear that never root, or set twrp, or unlock bootloader, because it is so risky. Thanks everyone so much. admin you can close the topic
i must say something too. i do know reason why my phone was bricked, maybe main reason is that when i first time survived phone and installed stock 6.0 firmware, then i try to re-lock bootloader, and after 6.0 to 7.0 install i got bricked. i say this because now when i installed bootloader, there is written oem_locked it means bootloader locked. looks like first time i locked bootloader, but screen was and is same (when i start up phone it says bootloader unlocked won't trust wait 5 seconds). so big thanks you guys
gioyocho said:
i must say something too. i do know reason why my phone was bricked, maybe main reason is that when i first time survived phone and installed stock 6.0 firmware, then i try to re-lock bootloader, and after 6.0 to 7.0 install i got bricked. i say this because now when i installed bootloader, there is written oem_locked it means bootloader locked. looks like first time i locked bootloader, but screen was and is same (when i start up phone it says bootloader unlocked won't trust wait 5 seconds). so big thanks you guys
Click to expand...
Click to collapse
Hmm, if you previously had stock Nougat on your device, you wouldn't have been able to lock your bootloader with the marshmallow firmware ( you need the stock firmware as new or newer than your Nougat bootloader).
Regardless, it's good that you got your device working again, just as a reminder, please if you do decide to flash old stock firmware, do not use old OTA updates, they are not safe to use on downgraded devices. We're lucky to have this blankflash leaked to us. If you flash old stock firmware, only use newer stock firmware to update.
echo92 said:
Hmm, if you previously had stock Nougat on your device, you wouldn't have been able to lock your bootloader with the marshmallow firmware ( you need the stock firmware as new or newer than your Nougat bootloader).
Regardless, it's good that you got your device working again, just as a reminder, please if you do decide to flash old stock firmware, do not use old OTA updates, they are not safe to use on downgraded devices. We're lucky to have this blankflash leaked to us. If you flash old stock firmware, only use newer stock firmware to update.
Click to expand...
Click to collapse
yes i do not know. it is strange situation. example now i had 2016 december security patch. came again ota update 1 april 2018 security patch and while installing finished again boot dead. and i survive again with newest rom. when i survive first time i just downloaded older bootloder file which was in the topic and that's why there was 2016 security patch. after download lastest rom with security patch and with new bootloader, and replace with new bootloader. now there is 1 april 2018 security patch
i guess ota updates is not safe
gioyocho said:
yes i do not know. it is strange situation. example now i had 2016 december security patch. came again ota update 1 april 2018 security patch and while installing finished again boot dead. and i survive again with newest rom. when i survive first time i just downloaded older bootloder file which was in the topic and that's why there was 2016 security patch. after download lastest rom with security patch and with new bootloader, and replace with new bootloader. now there is 1 april 2018 security patch
i guess ota updates is not safe
Click to expand...
Click to collapse
I'm confused, if you flashed the Dec 2016 stock ROM, the next update you'd have received would have likely been the March 2017 security patch OTA (NPJS25.93-14-4) update. How did you get the April 2018 OTA update? If your device had been on a previously newer build of stock Nougat, using that would have been a bad idea.
If you fully updated to the April 2018 security patch stock ROM, with the bootloader at version B1:07, you may be okay taking OTA updates. Please next time, double check the firmware you need. There's many sites with various firmwares and some of them can be quite old.
echo92 said:
I'm confused, if you flashed the Dec 2016 stock ROM, the next update you'd have received would have likely been the March 2017 security patch OTA (NPJS25.93-14-4) update. How did you get the April 2018 OTA update? If your device had been on a previously newer build of stock Nougat, using that would have been a bad idea.
If you fully updated to the April 2018 security patch stock ROM, with the bootloader at version B1:07, you may be okay taking OTA updates. Please next time, double check the firmware you need. There's many sites with various firmwares and some of them can be quite old.
Click to expand...
Click to collapse
No, i did not flashed 2016 stock rom, i flashed 2018 stock rom, but bootloader file was old, because i downloded it from old topic. when i replaced 2018 stock rom's bootloader file instead of old bootloader file, now i have 2018 1 april security patch. i think i can not install ota updates if them future come, because again my phone will be bricked
one reason is that if bootloader is unlocked, you do not have pemission to change something, but yesterday i installed ota update from 6.0 to 6.0.1 or security patch i do not know exactly, and while Nougat install finishes phone was bricked
gioyocho said:
Thanks for reply!
i had installed many drivers. even qualcomm and motorola, but situation is such. see file attachment. looks like my phone is in coma. i have windows 10. i will say long story short
1. i had android 8.1.0 RR, it was heating and i changed to RR 7.1.2. it worked good
2. it was also heating and i decides to change kernel and phone stop on RR logo, it was rounding but phone won't working. i had no backup or rom files
3. then i installed stock rom 6.0 marshmallow from fastboot with cmd, i downloded it from motorola's official site. i had 6.0 and bootloader unlocked. than came 6.0.1 ota and i updated it was ok. than came also ota update Nougat and installation process phone won't boot
Click to expand...
Click to collapse
just to be clear this all happened from RR 8.1.0? why did you not just follow what i said here and start your RR 7.1.2?
https://forum.xda-developers.com/showpost.php?p=76628308&postcount=1828
You could have saved yourself all the hassle
gioyocho said:
No, i did not flashed 2016 stock rom, i flashed 2018 stock rom, but bootloader file was old, because i downloded it from old topic. when i replaced 2018 stock rom's bootloader file instead of old bootloader file, now i have 2018 1 april security patch. i think i can not install ota updates if them future come, because again my phone will be bricked
one reason is that if bootloader is unlocked, you do not have pemission to change something, but yesterday i installed ota update from 6.0 to 6.0.1 or security patch i do not know exactly, and while Nougat install finishes phone was bricked
Click to expand...
Click to collapse
I'm still confused, you mentioned the December 2016 security patch (NPJ25.93-14), is that the firmware you were on before? I'm just trying to work out what firmware you had/were flashing on your device (since you mentioned Marshmallow 6.0.1 and then mentioned April 2018, there's a lot of builds inbetween those versions...)
I'm also confused by the reasoning for using the old bootloader file with the April 2018 stock ROM, can you explain the thinking behind mixing old and new firmware files, or have I misunderstood you?
You mentioned previously with bricking on the April 2018 OTA, what firmware version were you on then, if you can remember? I'm just curious as I've not heard of bricks on the April 2018 update yet.
The safest way to use OTA updates is to have your device formally on the same security patch level. In your case, you must ensure your device has the April 2018 B1:07 bootloader/GPT/system/modem etc. Doesn't matter if your bootloader is unlocked or locked (though a locked bootloader would strictly enforce having the same firmware patch level). Mixing firmwares is not a good idea for OTA updates as you found out. When you downgraded to Marshmallow, you likely did not downgrade your bootloader (your bootloader would have blocked the flashing of an older bootloader), so you had a Nougat bootloader but a Marshmallow system. Taking a Marshmallow or old Nougat OTA would have likely corrupted your newer Nougat bootloader (as OTA updates do not appear to check your bootloader version). Hence why you hard bricked then. I'm curious as to why this may have happened with the April 2018 OTA though.
Ayan Uchiha Choudhury said:
just to be clear this all happened from RR 8.1.0? why did you not just follow what i said here and start your RR 7.1.2?
https://forum.xda-developers.com/showpost.php?p=76628308&postcount=1828
You could have saved yourself all the hassle
Click to expand...
Click to collapse
Thanks for reply. your post was after i installed another kernel and i had bootloop

Need help rooting my phone. Model: SM-C9000 c9ltechn, 8.0 oreo Samsung experience 9.0

First of all, I want to tell you that I'm not very familiar with rooting but have just a bit experience flashing custom roms, so please go easy on me.
I have done some research and found a couple things that I couldn't find answers for:
1) First one is that apparently you need your bootloader unlocked/ OEM unlocking enabled in developer options, however since I upgraded to Oreo in last August, that option disappeared. I've tried two methods for making it appear that I've found online (keeping phone up for 7 days straight and reverting time back) but none worked. I've read somewhere that if you downgrade to Nougat, enable it then re update to Oreo your bootloader will remain unlocked. So, can someone confirm this? Can you downgrade with a locked bootloader? And if so, can someone guide me through it? (Additional question: will the downgrade reset user data?)
2) After unlocking bootloader you need to flash TWRP but I have so many questions on that. First: I couldn't find a TWRP for oreo. Does it work regardless of os version? Second: I found a guide from XDA that is written long ago, and it says "make a full backup of your system, including EFS before flashing". How do you backup without flashing it tho? All guides are about using either a custom recovery or rooted app.
3) Do you really need TWRP? I mean, can't you flash Magisk via Odin/ADB directly, perhaps without unlocking bootloader? What happens if I use install command from ADB?
4) So does tripping knox fuse achieve anything other than killing the nonexistent system updates and samsung guarantee? I want to make sure Samsung health is going to operate.

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