Interesting one. I gave it a try on both Ubuntu Mate 20.04 and Xubuntu 20.04 on my AMD desktop PC (GPU is Radeon VII) and I can confirm the issue.
Also, it seems others have the same issue, there is a post confirming this on Xubuntu Facebook and Reddit pages, together with a fix.
I am going to test install and run the fix, will report back later.