Do you have any displayport displays plugged in? If so, and you can switch to HDMI, that should get you online long enough to purge the driver, and manually install 460.73 from the driver archive - this is what I had to do, unfortunately.
Many of us have reported crashes on boot in Ubuntu 20.04 with the latest driver on this thread:
One of the Nvidia devs said they have managed to reproduce it and are actively working towards a fix, that was the last update as of Jun 2nd.