Some applications do not provide a window class according to the spec (WM_CLASS on X11, appId on Wayland), so KWin cannot "detect" this property.
In those cases, notify the user that this is a bug within the application (so it is not confused for a KWin misbehavior), and also prevent setting a wrong description.
BUG: 462644 FIXED-IN: 5.27
Previous commits are to improve the visuals of the error message with larger texts and use the proper
Kirigami.Dialog instead of an overlay sheet.