SUMMARY
***
Kwin_X11 constantly uses ridiculous amount of CPU. In extreme cases 60%. Must be dealt with top priority.
***

STEPS TO REPRODUCE
1. Open 50fps avc1 video via SMPlayer/mpv
2. Watch it in a) a window b) full screen
3. click Konsole (you removed ctrl+at+t, not my fault, you have to click, or type...)
5. type "top" (don't use htop, it calculates wrong...).

OBSERVED RESULT
Unacceptable extreme use of CPU by Kwin_X11


EXPECTED RESULT:

1. Revert the regression to make kwin operate as smoothly as in the times of KDE 5.x. This regression puts kwin and by extension, the whole KDE6 in an alpha stage "class". This is just Intel only, not even a "brand new, fancy" Nvidia/AMD/AMD APU. Just Intel.

Imagine this: kwin in current state and non-gpu-accelerated video (eg. AV1) and you have "kswapd0" disaster with lockdown/total freeze, even with zswap with z3fold (to which you should switch instead of using the wrong default) allocator and early module load of LZ4 (not zstd, which is the wrong default again, because of RAM and CPU usage,...).

2. Reinstate the settings of kwin in system setting (regression of settings, now its impossible to set any parameters of the compositor, the settings were completely removed in KDE6 - users can't chose Open GL version or set any other parameters, user doesn't know if kwin is using OpenGL v2 or 3. There are zero settings* , e.g. speed/smoothness trade-off settings were removed, but even if the the "trade-off" settings were there, in KD5 in the "smoothest" settings kwin was never eating CPU or like in this KDE6 case, kwin in KDE5 had never had a "CPU leakage"/constant CPU drainage). This is wrong, really wrong. 



SOFTWARE/OS VERSIONS
pacman -Qs:
local/kwin 6.0.5-2 (plasma) [older versions from KDE6 too]
local/kwindowsystem 6.2.0-1 (kf6)
local/kwindowsystem5 5.116.0-1 (kf5)

KDE Plasma Version: 6.0.5
KDE Frameworks Version: 6.2.0
Qt Version: 6.7.1
Kernel Version: 6.6.32-1-lts/6.8.x/6.9.x (6.9.x has nasty bugs...)
Graphics Platform: X11
Memory: 3.7 GiB of RAM
Graphics Processor: Mesa Intel HD

====
asterix notations:
*All was purposely removed to cater to the lowest "MS dumb user denominator" (just like double click instead of single click and "folder layout" instead of "desktop"; please don't put any distro users in the same category...!)
**KDE users use krunner and home folder (often on separate block device).