SUMMARY The output property of the window class is readonly https://invent.kde.org/plasma/kwin/-/blob/master/src/window.h#L109 . However there is a method to change this property on the workspacewrapper https://invent.kde.org/plasma/kwin/-/blob/master/src/scripting/workspace_wrapper.h?ref_type=heads#L370 it would be nicer if the api just allowed setting the output property on the window class instead of having to use this wrapper method. Side note: this workspace wrapper still has a lot of "client" everywhere, whereas the rest of the code base seems to have shifted from "client" in KWin 5 to "window" in KWin 6 (at least from my experience from what I've seen). So for consistency purposes it would be nice to rename all references to client in this file to window as well.
Hmm, not sure if having the property be writable directly makes sense, but some API on the window itself would certainly seem better.