A:Answer The differences are listed in the other questions. Long story short, if you buy the Steam version, you can only play it on Steam/PC as they are not compatible with each other and likely never will be.
If you buy the XBOX version of the game, you can install it on your PC and XBOX. To install in on your PC, you use the XBOX WINDOWS STORE APP and launch it directly through there as well.
There are guides on how to launch WINDOWS STORE games through Steam, but that's independent of this answer.
TLDR: If you want to play on PC and CONSOLE and only pay once, you MUST buy the XBOX version of the game.