IMHO, within PureOS Terminal is to be used: apt install xserver-xorg-video-nouveau (from /pureos amber main). https://nouveau.freedesktop.org/wiki/ NOTE:
If considering closed source drivers (apt purge above and adjust repo address), this guide makes some sense to me by adding / buster non-free (without main) repository, as described (usage of nvidia-detect, etc.). Continue to use GNOME on Xorg.