Thank you for your help!
Upon opening the 'Additional Drivers' app, the window reported that it
was using a manually installed driver (unclear which) and all other
driver options were grayed out. I followed the suggestion here
(https://askubuntu.com/questions/1237590/not-able-to-change-the-nvidia-
Public bug reported:
On every boot, system starts gdm.service but fails to load graphical
login interface. Instead, black screen with cursor appears, flashes
about 3 or 4 times, then hangs on a black screen with flashing cursor.
From this screen, I can Ctrl+Alt+F2 into tty2 and login. In order to
