At least to start. Microsoft strongly encourages all Xbox games to also come out on PC, though they sometimes release later. I cannot find any game developed originally for Xbox Series X|S where this hasn't happened eventually (and the developers definitively aren't still working on the PC version).

And they might eventually steer all games into XBox store.

I am expecting the day Microsoft decides to take all their studios out of Steam, if SteamOS starts to be too much of a pain.