Basically Kwin and other programs (simple xdg-desktop-portal or even gimp) crash and they bork the entire screen with no recovery other than rebooting. When the program that crash is Kwin it’s particularly bad because it happens at login.
I may have seen something similar, but it’s not consistent nor common. I’ve seen artifacting on KDE lockscreen and I think I’ve had 2 lockups since upgrading to plasma 6.
I’m in an AMD GPU (6650XT) with an older CPU (5600X) on an old motherboard (X370 from OG Ryzen launch).
If your have more details, I’ll see if I can repro. My system is pretty stable though, and I use my computer almost every day (kids use it to pay games, I do SW dev). It mostly just runs Firefox and Konsole, and sometimes Steam and a handful of other apps (Godot, Multi MC for Minecraft, some authenticator app I got from Flathub).
All the details I have are in the issue, it’s from me. I have also reported it to kde through Konqi and to fedora through GnomeAbrt
I’ll check it out later, but I’m guessing I won’t be able to reproduce it since mine isn’t Vega. I do have a laptop with a Vega APU, so I could try that (might have time tonight).
My machines are running Tumbleweed on KDE 6, so if I can repro it means it’s not a Fedora-specific issue.