Walter's post is an interesting one in that it may explain my problem with 20.04.1. (The problem is that it hangs on shut down.)
The installer would not finish if I chose to install third-party drivers. It would only finish if I didn't do that (and this turned out to be a known bug with the 20.04.01 installer).
Basically everything is fine with my 20.04.1 install (it's on an external drive) except that it won't shut down.
(The error message I get is: DRM: GPU lockup - switching to software fbcon.)
I am using a somewhat older graphics card: the NVIDIA GF106 GeForce GTS 450, with the 390.138 driver, but it's worked fine so far.
The driver is the correct one for the card, and the card, I believe, is the newest one (or among the newest) that my machine will accommodate.
If I could get 20.04 to shut down properly, I'd be fine. (It does reboot with no problem.) My card and driver work fine on Ubuntu-MATE 18.04.
But from reading Walter's post above, I'm starting to think that 20.04 has left the 390 driver behind. Or the latest kernels, or whatever, have left it behind.
Does anyone know anything more about this? I explain the situation further in a recent post here.