Existing Android 10 builds has a critical problem, that allowed us to flash or erase any bootloader partition even if the bootloader is not unlocked. However, Android 11 builds blocked this method.
Therefore, I think it's time to disclose the unlock method now. It's known working on both TA-1243 and TA-1251.
The critical part for unlocking the bootloader is - the prototype bootloader of this phone. By opportunity, I got the early bootloader from a prototype unit that allows us to unlock the bootloader, thanks to the help of a Canadian people who claimed to have a Nokia 8.3 prototype himself.
Your warranty will be void as bootloader unlock is not reverseable - you cannot relock it. We didn't try this method on Nokia 8 V 5G UW due to lack of units, so take your own risk if you wanted to give it a try. You've been warned.
To use this method, you need to ensure your phone has Android 10 installed - the latest build that we can use this method is 00WW_1_150-B01, you can confirm this by dialing *#*#7837#*#*.
If your phone has Android 11 installed (00WW_2_180-B01 or newer), then this bootloader unlock method has been blocked, but there's known workaround for this. Check 2nd reply for details.
Please download the prototype bootloader from here:
Then flash it under fastboot mode, and unlock the bootloader - pretty simple:
fastboot flash abl abl_proto.elf fastboot reboot-bootloader fastboot oem unlock-go
Confirm unlock on your phone and it's all done. You can safely update the phone to Android 11 right after unlocked. Since we cannot perform critical unlock properly, we can only do regular unlock, but this should be enough.
Have fun for modding this device!