https://bugs.freedesktop.org/show_bug.cgi?id=91416
--- Comment #6 from Markus Mitsch markusmitsch86@gmail.com --- ok. thanks for the tips, it works now. i set the kwin compositor to: (option names may differ, i have a german machine)
-scaling: precise -opengl instead of xrender -glx not egl -vsync to automatic -window thumbnails: only visible windows -compositor not deactivated in fullscreen -no color correction