Many other GUI environments' window managers implement a feature whereby while switching windows or apps, you can close the current one via a key on the keyboard without leaving the Task Switcher: macOS: while switcher is open, quit app with Q key Unity: while switcher is open, quit app with Q key GNOME: while switcher is open, close window with W or F4 key This is a great productivity booster and it would be absolutely lovely if KWin had the same feature. I would propose closing the current window with the W key, and quitting its parent app with the Q key.
I expected this request when I heard that GNOME supports this. Personally I don't think it makes any sense to use the task switcher for window closing, but I would not oppose to a patch.
For what is worth to mention: the backend supports closing a window and exports it the QtQuick side. Just do: model.close(currentIndex) from Qml side to close the currently selected window.
*** This bug has been marked as a duplicate of bug 308331 ***