Random black windows after Plasma 6 upgrade

I’m getting windows randomly flashing to black since the upgrade to Plasma 6 (on KDE Neon) . The black out happens a lot if I am interacting with a different window but don’t really see a set pattern of what causes it other than it seems tied to keyboard entry or mouse movement. I am getting lag sometimes on keyboard entry as well. Never seen it before - I assume this is related to the switch to wayland? This machine has an old nvidia card. Any ideas how to fix? Or alternatively how do I switch back to X11?

Edit: I upgraded from nvidia-driver-535 to nvidia-driver-545 and now the system is basically unusable due to the lag and I still get the black windows. It takes about 10 seconds for a character to appear when I type. top shows plenty of CPU and memory available.

Edit 2: I managed to switch back to X11 through the login screen / behavior in system settings… but in order to use that I was required to bypass the login prompt? Is there a way to do it without turning on auto-login? Switching back to X11 did fix the terrible lag and black windows btw.

Random black windows / rending errors and better behavior on X11 do sound like a GPU-related issue unfortunately.

If you disable auto-login, you can select whether to use the Wayland or X11 session through the easy-to-miss dropdown on the bottom left of the SDDM login screen. SDDM will remember the new setting once you log in with the different session type.