SUMMARY
The commit https://invent.kde.org/plasma/kwin/-/commit/23806d31e23d2ef2bc8344114feb6d27364cdc01 has introduced a regression that can be observed on my system that manifests itself as KWin taking up 100% of a single CPU core (and dropping frames) when screencasting.

Reverting the mentioned commit has completely resolved the issue for me.

STEPS TO REPRODUCE
0. Log in to Plasma Wayland session
1. Begin screencasting (I used rectangular region which is scheduled for 6.0, but fullscreen produced the same issue for me - I used OBS to test this)

OBSERVED RESULT
KWin takes up 100% of a singe CPU core (thread), mouse movement is choppy, and journalctl --user shows KWin is struggling with frame drops.

EXPECTED RESULT
Screencasting is smooth, does not impact desktop usage, and does not take 100% of a single CPU core.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: NixOS
(available in About System)
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9

ADDITIONAL INFORMATION
-