SUMMARY

When using kwin_wayland, windows which use transparency with background blur flicker during screen updates and the mouse point may leave square blocks of trails in the background color (as if no background blur was used). This can be observed both with NVIDIA and Intel. Disabling background blur in konsole fixes the issue but other windows may (and even the plasma panels) may still be affected, tho the problem is most prominent with konsole.


STEPS TO REPRODUCE
1. Enable background transparency/blur in konsole
2. Update screen contents in konsole and move the mouse point around within the window
3. Move the window around

OBSERVED RESULT

Trails of background-colored blocks are left behind the mouse cursor, konsole window contents may flicker heavily.

EXPECTED RESULT

No flickering, no mouse trails.

SOFTWARE/OS VERSIONS

Operating System: Gentoo Linux 2.13
KDE Plasma Version: 5.27.4
KDE Frameworks Version: 5.105.0
Qt Version: 5.15.9
Kernel Version: 6.1.26-gentoo (64-bit)
Graphics Platform: X11
Processors: 20 × 12th Gen Intel® Core™ i7-12700K
Memory: 31.1 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 3080 Ti/PCIe/SSE2
Manufacturer: ASRock
Product Name: Z690 Pro RS

ADDITIONAL INFORMATION

Also happens with Intel (Gen3 iGPU): Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz

But usually, flickering cannot be observed with latest Plasma version but mouse trails are still present. The flicker problem mostly went away after I bumped the iGPU shared memory area from 32 to 512 MB (and it also fixed the lockscreen freezing until I "loginctl unlock-session" from alt+F2 and restart kwin which is not feasible with wayland).

I disabled konsole background blur on that iGPU for now because it really hurts desktop rendering performance, so it less a problem on that iGPU anyways for me which mostly lefts us with the issue on NVIDIA.