Oh, that’s my mistake. I could have sworn it included packages for Eoan. Try Oibaf’s PPA instead: https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers?field.series_filter=eoan
Also, if you have openssh-server installed, you should be able to access a terminal on your machine even when the display is totally broken using the ssh command from another Linux machine or using PuTTY on Windows.
Should it break again, try logging in with
ssh <username>@<IP address or hostname>
omitting the angle brackets, of course.
Alternatively, try to access a virtual terminal by hitting one of CTRL+ALT+F[2-6] and waiting a couple seconds. (Usually the display server lives on VT7 or VT1, so you can get back to it with CTRL+ALT+F7 or CTRL+ALT+F1).
then look through the output of dmesg | less (jump to the end by typing G , or back to the beginning using g) and look for errors that mention your GPU.
Also take a look at the Xorg log at /var/log/Xorg.0.log for similar.