Can you load a recovery kernel from Advanced Options for Ubuntu? If so, then select Network to get a connection to the internet. Then select Root to get to a root shell (terminal). We exit the command line and get back to the recovery menu by typing exit.

At the root shell we can remove the Nvidia driver with

Code:
apt remove --purge nvidia*
When back at the recovery menu Resume will load the Ubuntu desktop with an open source video driver. If you get a black screen, then re-boot. If you cannot load a recovery kernel you may have work from a Live session to install a 5.4 kernel.

Regards.