FWIW, there was a KDE bug (Plasma version 6.1) discussing an issue with triple buffering causing stuttering for some users. This was apparently resolved, but some users still experience it with Plasma version 6.2 and disable it via an environment variable…
https://bbs.archlinux.org/viewtopic.php?id=300186
https://bbs.archlinux.org/viewtopic.php?id=300234
Other than that I’m not sure there is much you can do apart from reporting it as a bug.