I've upgraded to Windows 11 to test a couple of things. The integration of Xbox app is different then on Windows 10, which is fine. After downloading the Windows Xbox App from the Windows store, then finding your friend playing SoT, right clicking and then "Join Game" does start up SoT, after the initial logo's at startup, it asks you if I want to join the game, but after saying yes, it just puts me to the "Start Game" screen.
Similar issue if game is already started, it just stays at the screen I already was at when clicking yes to join the game.
I am running the Steam version btw.