Recovering a system with bad Nvidia GPU configuration.
Depending on your system it can be - somewhat - complicated to reach that point.
Using encryption and btrfs is all factors that add steps to reach the goal of recovering from a bad configuration.
The primary steps is to get into the system - this is described in the basic recovery guide - where you will end in what is called a chroot environment - I won’t go into those details - the recovery guide outlines those details.
The following assume you have mounted the system and entered the chroot environment.
When the bad configuration has been caused by envycontrol - you can run envycontrol to remove the changes made.
envycontrol --reset
Then exit the chroot
exit
And restart
reboot