When you run a Plasma Wayland session with on an old computer, putting your
computer to hibernation, sleep or doing simple VT switch, causes severe picture
distortion on computer screen, making it useless. The only solution to it is to
kill kwin_wayland and restart session.
I don't know if it's compositor's fault or drivers, but X11 session works fine.

openSUSE Leap 15.6, Plasma 5.27.11.
Hardware is Mobility Radeon HD2600 aka M76/RV630.
There is no suspicions messages in kernel or kwin log, pointing to a problem.