STEPS TO REPRODUCE
1. Login to plasma wayland
2. Open any(?) game that will be gpu bound, ive personally tested Rocket League (steam version, proton) and Risk of Rain 2 (steam, proton).
3. Ensure vsync is disabled, i've notice if vsync is on then kwin renders at its intended framerate


OBSERVED RESULT
Kwin will render (based on the show fps desktop effect) at roughly half the framerate of the game.  For example, in Rocket League the game renders at about ~300 fps, then kwin will render at about 150.  In Risk of Rain 2, the game will run at about 135 fps and kwin will render at about 75.  This has a very noticeable impact on visual quality, as the framerate is being nearly halfed.

EXPECTED RESULT
Kwin should render at roughly the games framerate, which is what it does if i enable vsync.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: gentoo / git master using kdesrc build
KDE Plasma Version:  git master
KDE Frameworks Version: git master
Qt Version: 6.6.1 from gentoo packages

ADDITIONAL INFORMATION

Kwin wayland works as intended on version 5.27.10.
GPU: 5700xt, mesa git
CPU: 12900k
Monitor: 1440p 240hz LG 27GR95QE