Halo Infinite is pretty good! Developer 343 Industries seems to have left the shadow of Bungie behind and built a new foundation for the series, but one unfortunate aspect that's come to light following the game's full launch (after the surprise multiplayer release several weeks ago) is that the cross-save functionality with consoles only works if you've bought the game via the Microsoft store or Xbox Game Pass.
This is a bit bizarre. PC Gamer tested this by loading up Infinite on Steam using the same Microsoft account that had been used on an Xbox Series X to play the campaign. An achievement popped and an 'end current session to play here' notification appeared, but the save isn't there.
This may only affect a minority of players but does somewhat isolate the Steam version of the game, and feels a little like Xbox trying to nudge players in the Game Pass direction. It seems like cross-save should be able to work smoothly across platforms when crossplay multiplayer does—and the Master Chief Collection is also able to sync saves between Steam, Microsoft Store, and Xbox. But this isn't a first for a Microsoft game: Forza Horizon 5's cross-save functionality doesn't work on Steam, either.
So if you're going to buy Halo Infinite and want to use the cross-play feature, careful where you buy it. Yes this stuff is stupid. I've contacted Xbox PR about it and will update with any response.