I got the problem on Arch with KDE Plasma and on Debian with KDE Plasma.
→ simple solution:
I mounted a key in keyboard shortcuts of plasma and set up the following command behind it:
systemctl poweroff && wineserver -k
I use the key to shutdown the system (Im to lazy to use the mouse and click on shutdown). I have used a special key for it to not happen as a accident.
Systemd didn’t work, because of wineserver running as user and systemd was not cooperative on that matter.