Oh indeed. But then this was the wrong thing to use anyway. You don't want to center the window in relation to the combined geometry, as the documentation of QDesktopWidget rightfully says.
Not that I really understand this code, I admit.
Oh I see.
Is there a non-deprecated method to get the overall geometry of all screens combined, or do we need to iterate over the list of screens?
Surprising that this doesn't seem to be anywhere in the API .... !?
Fix pushed https://commits.kde.org/plasma-desktop/2b5e86323f180f0c51ef9af898a69a522bc379ad after the bug reporter confirmed it fixes the bug.
Reopening this after it was committed is a bit weird. I can't close it, please do.