Some Xwayland applications cannot be closed on Wayland e.g. via ALT + F3 or with right click on the task bar. The close button is somehow disabled. The only possibility to close them is via the system monitor (ksysguard). I've had this issue with several XWayland applications that crashed especially on Wine/Proton. If I find a way to always run into this issue I will add it here. Plasma 5.13.4 KDE Frameworks 5.49 Qt 5.11.1 Wayland 1.16 XWayland 1.20.1
Still a problem? Name one example application I can try with. Best would be an open source app.
I can't specifically name one application as it happened with crashed ones on Wine. Will close this now and make a report if I can nail this down.