It depends how you interpret this. MS has released games on multiple systems in the past and they were looking into a case by case basis.
On the other hand, it never made sense to me to purchase Zenimax and ABK only to limit them on Xbox platform. Those are decades old third party IP. Its like buying EA and keeping FC on a single console... it doesn't make sense business wise. I can't imagine TES 6 will be exclusive. Starfield didn't cause the wave MS needed, they were in hindsight better off with it as a multiplatform game.
Sea of Thieves I can totally see happening since its a GaaS game, such as Sony offering Destiny on Xbox.