When it says Steam to Xbox cross-platform in September, does that also mean steam to gamepass? Or is that already possible? I have the game on gamepass and I have been having a lot of fun with it so far, I prefer to use steam and would probably purchase it there if I were able to keep my progress on the gamepads version.
Progress is synced within Microsoft ecosystem platforms, but not to Steam.
Crossplay is currently possible between Microsoft ecosystem platforms (between Xbox One, Xbox Series X/S, and Win10).
The Steam to Xbox crossplay coming in September is crossplay between Steam and Microsoft ecosystem platforms (Xbox), this is currently not in the game.