No idea what to do, but a short "me too"
. Other settings than those under display work well, but on entering submenu 'compositor' or 'gamma', systemsettings immediately crash.
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EDIT: When I go to a terminal and enter
kcmshell5 kwincompositing
the compositor settings dialog opens, and changes can be made and applied. (kcmshell5 --list gives an overview of all systemsetting modules).