I’m posting this here in the Kde Plasma section, because the problem seems to be KDE specific. Here is a link to my old post in the Graphics & Display category: Screen Tearing while Gaming with Optimus (short summary, Laptop with intel and nvidia graphic, optimus -> hybrid driver 455 installed, get screen tearing while gaming on games with high framerate)
I now have Manjaro Kde and Manjaro XFCE installed side by side and on XFCE i get no screen tearing while playing Games with high frames, like CS:GO. On Kde I still get really bad screen tearing. The setup on both of those installs was exactly the same.
I have a slight suspicion that it has something to do with the compositor. When I’m on Kde and press the key comination alt+shift+f12 to reset the compositor, the screen tearing gets better for a second before getting worse again.
I then tried to change the settings in the compositor section in the settings and un- and rechecking the box for allowing programs to deactivate compositor, but nothing seems to help :(.
I would really like to have it working on Manjaro Kde, XFCE just is not my thing to put it mildly ;).