If drivers fail to load at boot

Your machine boots up with a low-resolution screen, and and after logging in you see an error message to the effect  of “Your system is currently running without video acceleration. You may experience poor performance and high CPU usage“.

There should also be a button to launch the driver manager.

If you’re unable to change things via the driver manager:

From a shell: edit /etc/modules

Make sure the following three lines are there – if not, add them to the bottom of the file:

nvidia
nvidia-drm
nvidia-modeset

Then reboot.

If that doesn’t work, you can see what the system uses with
ubuntu-devices list

You can use ubuntu-devices autoinstall which should do the job.
Reboot when complete.

Or you can install a specific driver version with

apt install nvidia-driver-470 (or what ever version you need). You can use ubuntu-devices list to see available choices. Reboot when complete.

To remove the driver and its associated dependencies, use apt.
Ex.
sudo apt remove nvidia-driver-470
sudo apt autoremove
Then reboot. It should then use the open-source nouveau driver.

You can install the open-source driver to revert to the open-source driver:

sudo apt install xserver-xorg-video-nouveau
Then reboot