"New Score" Window + tab key
1 Once started musescore 4, click on "New Score".
2 Then, use the "tab" key.
The selection moves to the window behind ("Musescore 4"), instead of the active one. It is more easy to see the selection square by pressing a second time. It appears at "&file", and loops around on the main window.
The intended movement would be to move around the "New Score" window's menus.