SUMMARY

After updating from Plasma 6.4.5 to Plasma 6.5.0, I noticed that my osu! lazer is stuttering. The game is barely playable.

osu-lazer uses SDL2, or optionally SDL3 under-the-hood (setting environment variable OSU_SDL3=true). It's rendering using an OpenGL renderer, or an experimental Vulkan renderer. No matter the combination of SDL and renderer, the game stutters when playing a song. The Vulkan renderer is even glitching out with flickering, black frames whenever the stutters occur. Changing FPS limit also does not change anything. Switching from multithreaded rendering to singlethreaded rendering does not change anything. SDL has an environment variable called SDL_VIDEODRIVER. Setting it to "wayland" enables native Wayland support. Setting or not setting this also does not change anything.

The game does not stutter in song select or the main menu. Only when playing a song. It also does not stutter in window mode, only in borderless window and fullscreen. The stutters do not occur when the song has an "idle" part and you're not clicking any objects. So it could also be related to sound or keyboard/mouse input.

I ruled out updates of other programs that I use. I bisected the nixpkgs repo and built my NixOS installation against the individual commits while iterating through them. The first bad commit with stutters is https://github.com/NixOS/nixpkgs/commit/15729ec4e1b90abbcec33b75c68d35dd5b968453, which is the update from Plasma 6.4.5 to 6.5.0 in NixOS.

I am using an AMD Radeon RX 7900 XTX with mesa 25.2.5.

I have not tried osu on Arch, so I can't rule out that it is NixOS specific. Furthermore, I have a friend who is using CachyOS on Nvidia, and he is not experiencing these stutters.

Here's a video of it. It's hard to see on the video, but you can clearly see the lag spikes in the "draw" section of the debug overlay.
https://youtu.be/ehJCY15L4ww

STEPS TO REPRODUCE
1. Open osu! lazer
2. Select and start a song
3. Play

OBSERVED RESULT
Experience stutters whenever hitting circles/sliders

EXPECTED RESULT
No stutters whenever hitting circles/sliders

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Linux 6.17.2-zen, NixOS 25.11 (nixos-unstable, commit 08dacfca559e1d7da38f3cf05f1f45ee9bfd213c)
KDE Plasma Version: 6.5.0
KDE Frameworks Version: 6.19.0
Qt Version: 6.10.0
GPU: AMD Radeon RX 7900 XTX
Mesa: 25.2.5