Microsoft Confirms Plans To Release Xbox First Party Games “Across All Platforms”, Including PlayStation

Definitely won't be all of them. Probably just a small set that are not huge money makers. They already publish some titles as third party, like Minecraft, Ori, and Lucky's Tale.

Guessing we just get ports of, like, Hi-Fi Rush and Psychonauts, and continued support of some Activision titles that are 3rd party like Diablo 4, Spyro, Crash, and a token Call of Duty game.