Expected behavior
Pressing Ctrl + W closes the window of the desktop-app, but not the entire app, like clicking the close-button of the window.
Actual behavior
Pressing Ctrl + W does nothing.
Ctrl + Q does close the app entirely, so that notifications of received messages cannot be shown immediately; which is often preferable for me, but it does depend on the situation.
Many other apps that i use (for example: GNOME-apps, Element, Thunderbird, and Firefox) close the current window/tab when pressing Ctrl + W. Element can remain open in the background when it was closed with Ctrl + W, but Ctrl + Q closes it entirely.
Using Alt + F4 works like i requested, but, at least for me, it is less practical than clicking the close-button, due to the inconvenient placement of those keys (which is even less convenient on a keyboard which has another key, like Alt Gr, instead of a second Alt-key).