From: jamm on

kwriteconfig --file kwinrc --group Compositing --key RefreshRate 120

...bumps the refresh rate from 50 up to 120. New one to me, I thought others
might find it useful. :)

--
*From the 1966 TV series:*
Robin: You can't get away from Batman that easy!
Batman: Easily.
Robin: Easily.
Batman: Good grammar is essential, Robin.