Woo! Glad you got it backed up before abandoning ship. 
I'm not sure what happened but it sounds frustrating to say the least.
Maybe install POP!_OS the AMD version if you want to try that card again. Also consider Debian 11 you can choose what desktop-
environment(s) you want or create a minimal base system and install only the necessary packages & dependencies.
You said "never again with AMD cards in Ubuntu" but I hope later on you can get it to work on your test rig.
I'm not sure what happened but it sounds frustrating to say the least. Maybe install POP!_OS the AMD version if you want to try that card again. Also consider Debian 11 you can choose what desktop-
environment(s) you want or create a minimal base system and install only the necessary packages & dependencies.
You said "never again with AMD cards in Ubuntu" but I hope later on you can get it to work on your test rig.