On MX Linux 17 I encountered the same error having installed KWin via Synaptic Package Manager. After some digging, I launched the Window Manager Settings via the terminal:
Code:
/usr/bin/kcmshell5 --icon preferences-system-windows kwindecoration kwinactions kwinfocus kwinmoving kwinadvanced kwinrules kwincompositing kwineffects kwintabbox kwinscreenedges kwinscripts
. In the terminal I found a couple messages referring to programs it couldn't launch when I clicked
Get New Decoartions.... After I read online about the messages I installed
kwin-cli-tools and later
kinit and
kded5 via Synaptic Package Manager.
I no longer have the issue.