Created attachment 161660 [details]
clear example of a visual bug in the popup menu

SUMMARY
I have 2 monitors - primary 2560x1600 with 150% scale and second 1920x1080 with 100% scale. The second monitor is set in the settings to the right of the main monitor. If you call a pop-up menu on the second monitor by right-clicking on an empty space on the desktop or somewhere on the taskbar, the frame of this window can become transparent when the mouse cursor approaches it. Or all buttons may disappear and be displayed only when the mouse cursor is over them. 
If I put the second monitor in settings to the left of the main monitor - the same problem will occur on the main monitor. I created a new user and did the steps from "STEPS TO REPRODUCE" there but it didn't fix the bug. I also tried to install the latest stable KDE Neon and got the same problem there.


STEPS TO REPRODUCE
1. Use Wayland session
2. Set scale of primary monitor to 150%
3. Connect second monitor
4. Place second monitor the left of the main monitor in the settings
5. Set scale of second monitor to 100%
6. Right-click on an empty space on the desktop of the left monitor and pull the mouse down on the menu that pops up

OBSERVED RESULT
Buttons in popup menu disappear and appear only when mouse cursor is pointing them. Sometimes the buttons don't disappear, but then the frame of the popup menu becomes transparent when the cursor approaches them

EXPECTED RESULT
Both frames and buttons must be visible until the popup menu loses focus

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora Linux 38 
KDE Plasma Version: 5.27.8
KDE Frameworks Version: 5.109.0
Qt Version: 5.15.10