On Wayland, screen rotation works for me if I uncheck "Only in tablet mode". If I check it, then rotation never works, even when in tablet mode. I know that tablet mode is correctly detected because when I fold my convertible laptop to enter tablet mode, the System Settings sidebar list items become larger as expected. So the Kirigami.Settings.tabletMode property is updating correctly. But whatever in KScreen watches this is not doing it properly.
Confirmed on Fedora 34 with all updates applied. "Only when in tablet mode." must be unticked for me to get automatic screen rotation.
*** This bug has been marked as a duplicate of bug 428626 ***