SUMMARY
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I put it under "major", beacuse kwin_x11 has a huge regression. Just noticed (when did it happen?): kwin_x11 is using 30% CPU either with blocking or without "blocking compositing by applications" in compositing settings. Ont top of this the default option: "allow applications to block compositing" is making video playback (typical avc1 with camera movement form left to right) completely lose Vsycn to blank. Un-tick the settings and compositing works trying to compensate, but barely makes it (not to smooth vsync to blank). It didn't use to be like this in the past at all.  Read below:
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STEPS TO REPRODUCE AND OBSERVED Resuslt
1. Play a typical video encoded in AVC1 where camera moves from left to right
2. Use $ mpv hwdec=vaapi vo=gpu to just do this
3. Observe complete lack of vsync and high kwin usage (both ticked and unticked)

EXPECTED RESULT
Revert changes to kwin_x11 as they used to be in the past: low CPU usage, smooth transitions (smooth transitions in settings do not make transitions as smooth as they were in the past -kwin_x11/compositing is broken), sync to vblank (vsync) working. Focusing on wayland doesn't mean brake X11. Please revert the changes and reinstate previous kwin_x11/compositing. The best version was the one that had chose OpenGL version in settings (OpenGLv3 was working the best). Now everything is broken. 

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 5.27.6
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.10

ADDITIONAL INFORMATION
X11
Intel only