Cleaning Up A Broken NVidia Installation

remove the current nvidia driver running

sudo apt purge nvidia-* && sudo apt autoremove

note the version of the nvidia driver you're removing, say nvidia-xyz

blacklist nouveau by opening /etc/modprobe.d/blacklist-nouveau.conf with your favourite editor and inserting

blacklist nouveau
blacklist lbm-nouveau
options nouveau modeset=0
alias nouveau off
alias lbm-nouveau off

Disabling the kernel nouveau (not sure whether this is necessary, though, but it does not seem to do harm to the installation)

echo options nouveau modeset=0 | sudo tee -a /etc/modprobe.d/nouveau-kms.conf
sudo update-initramfs -u

Reboot the computer and login to a terminal without display manager, e.g., CTRL+ALT+F1. Unfortunately, the display manager has been started already (still available under CTRL+ALT+F7), thus the service need to be stopped

sudo service lightdm stop

Activating gdm (gdm3) as default display manager.

sudo dpkg-reconfigure gdm3

This will return an error saying that the service has not been started and hence the display manager could not be switched. No worries, the switch will be carried out upon reboot.

Re-installing the nvidia driver that has been removed earlier, where xyz is the version that was uninstalled under the first step.

sudo apt install nvidia-xyz

Reboot your system

sudo shutdown -r now