One part is already documented. The bootloader unlock procedure: ✏ FP3: unlock the bootloader
As the article says:
Be aware: you will loose all your data and maybe the warranty of your phone, do this at your own risks
Thanks. Now we need a recovery like TWRP to use root managers like e.g magisk (https://forum.xda-developers.com/apps/magisk/official-magisk-v7-universal-systemless-t3473445)