Bug 493073

SUMMARY
Dynamic triple buffering sometimes drops the frame-rate to what feels like 20 fps. It will mostly stay there if you use the system at all, with sometimes a couple seconds of smooth 120fps

STEPS TO REPRODUCE
1. Have this Laptop, or possibly any 120Hz laptop with Radeon 880M
2. Boot your system, do anything like scroll a webpage open panel applets 
3. Notice the very low framerate, even when just moving the cursor

The kernel version might be important, with I can't test with older kernels because they don't work right with the hardware.

OBSERVED RESULT
kwin seems to switch between rendering okay and then suddenly, without being under any significantload dropping frames massively, and staying there even while idle. That's not something that should happen with working hw-decode on one of the most powerful iGPUs to date.
When measuring with the "Show FPS" effect kwin reports 52fps but I don't trust it. It feels more like 20fps, probably due to the frame timing. Those reportedly 52 fps do stay suspiciously constant too (when it's doing the thing).
I suspect something with the hysteresis is wrong, which makes kwin not want to go back once it starts triple buffering. Maybe triple buffering is just crazy expensive with this GPU so it mostly can't go back except for the occasional blip, but that's just a guess. 

An oddity I've seen is that you can sometimes see a config option for VRR in Display Configuration, but sometimes it's gone. To remove this variable I keep it is set to "never".

EXPECTED RESULT
A smooth 120fps with maybe a couple frames dropped at most during light webbrowsing, not stuttering along with what feels like 20

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.1.5
KDE Frameworks Version: 6.5.0
Qt Version: 6.7.2
Kernel Version: 6.11.0-rc7-3-mainline-um5606-dirty (64-bit)
Graphics Platform: Wayland
Processors: 20 × AMD Ryzen AI 9 365 w/ Radeon 880M
Memory: 22.6 GiB of RAM
Graphics Processor: AMD Radeon Graphics
Manufacturer: ASUSTeK COMPUTER INC.
Product Name: ASUS Zenbook S 16 UM5606WA_UM5606WA

ADDITIONAL INFORMATION
Somebody else with similar hardware also had this exact problem: https://github.com/BNieuwenhuizen/zenbook-s16/issues/7
I've set severity major because most of the time you can't even really watch videos fullscreen without very noticable stuttering, or move the cursor. Also, a lot more people will have this gpu pretty soon, seeing as it launched a month ago.
If this isn't easy to fix (which it might not be), please at least expose the setting as an option (since Plasma 6.1 the whole compositor kcm page is gone?), but idk.