SUMMARY Using an nvidia wayland session, various things result in brief rendering artifacts on the desktop. STEPS TO REPRODUCE 1. Start a nvidia wayland session 2. Open the calendar applet from the panel 3. Close the calendar applet by clicking away OBSERVED RESULT The "center" 1/8th or so of the calendar applet remains on the screen briefly. EXPECTED RESULT The entire calendar applet renders without any artifacts as it would under X11.
The Nvidia driver had some huge changes and how it interacts with KWin. Please try again and file new bugs as appropriate thank you!