Ubuntu - GPU - NVIDIA GPU - Uninstall NVIDIA driver

sudo dpkg -P $(dpkg -l | grep nvidia-driver | awk '{print $2}')
sudo apt autoremove

or

sudo apt remove nvidia-driver-470

sudo bash NVIDIA-Linux-x86_64-XXX.XX.run --uninstall

Enable Nouveau modules, if this was blacklisted previously:

sudo rm /etc/modprobe.d/blacklist-nvidia-nouveau.conf

else install the nouveau driver:

sudo apt update
 
sudo apt install xserver-xorg-video-nouveau # for xserver.

sudo reboot

or

sudo init 6

lsmod | grep nouveau

returns:

nouveau              1949696  4
mxm_wmi                16384  1 nouveau
ttm                   106496  1 nouveau
drm_kms_helper        184320  1 nouveau
drm                   491520  7 drm_kms_helper,ttm,nouveau
i2c_algo_bit           16384  1 nouveau
wmi                    32768  3 wmi_bmof,mxm_wmi,nouveau
video                  49152  1 nouveau