Howdy everyone!
Thanks for being patient with me. I’ve spent a bit of time looking into this and have some early findings I’d like to share in regards to system slowdowns occurring in KDE during video playback.
I was able to replicate the issue of KDE suddenly becoming slow under video playback. I was able to make this happen with Dragon Player and Haruna, as well as in Chromium-based browsers, but I was not able to replicate it in Firefox, mpv, or VLC. This slowdown only seems to occur with Adaptive Sync set to “Always” in display settings. My early educated guess at this point is that there’s something about these apps in particular that is causing the system’s frame rate to be brought down to match the frame rate of certain video sources. It does not appear to be caused by QT because VLC works fine, and it does not appear to be a libmpv related issue because mpv itself does not cause this behavior.
For now, I don’t seem to be able to replicate the behavior in a fully updated stock install of Fedora 41’s KDE spin with Adaptive Sync set to “Automatic”. If anybody has any more details about replicating this issue or conditions under which they see it happening, I’ll be keeping an eye on this thread.