Cannot install nvidia-390 driver, ubuntu 21

  Administration

Run sudo /usr/bin/nvidia-uninstall to uninstall a manually installed driver, if you still got one.

Remove everything of your old NVIDIA driver (simulate first):

sudo apt remove --purge -s nvidia-*
sudo apt remove --purge -s libnvidia-*

If only nvidia packages are there to be removed, remove really:

sudo apt remove --purge nvidia-*
sudo apt remove --purge libnvidia-*

Run sudo apt update and ubuntu-drivers devices again.

If nvidia-390 is still recommended, add your output of sudo ubuntu-drivers autoinstall again.