I never had such a problem with my old laptop (which had a burnt out nVidia GPU and was running on the Intel iGPU), so could it be a regression with Wayland.

I gotta check this out. Guess I'm going to wear down a DP connector this week!

I can no longer check it on the Laptop though (died), but on my AMD system, so at least if the problem is actually KDE, it should show up. Otherwise, I'll just count myself unlucky and unable to reproduce.