SUMMARY
On kwin 6.2.2 and above, starting a VR runtime with a wired PCVR headset connected (such as SteamVR or Monado, with the Valve Index VR headset) causes desktop performance to drop.

STEPS TO REPRODUCE
1. Install kwin/KDE 6.2.2 or newer
2. Plug in a wired VR headset (such as the Valve Index)
3. Start a VR runtime, like SteamVR or Monado

OBSERVED RESULT
Desktop performance becomes unusable while the runtime is open and performing actions such as moving the mouse (as seen in the attached video using Envision with Monado and a Valve Index)

EXPECTED RESULT
Desktop performance remains the same/similar with and without a VR runtime open.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.2.3
KDE Frameworks Version: 6.8.0
Qt Version: 6.8.0
Kernel Version: 6.11.6-zen1-1-zen (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 5600 6-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 6800 XT

ADDITIONAL INFORMATION
I have narrowed down the issue to specifically MR 6633 in kwin: https://invent.kde.org/plasma/kwin/-/merge_requests/6633
kwin v6.2.1.1 does not have this issue, neither does kwin v6.2.3 with MR 6633 reverted.