The FAQ says that players will be prompted to link the two the first time they load the game. And if you unlink later, you “will be constrained to relinking to only that specific and originally linked” Microsoft account.
The requirement stings given that there’s no cross-platform saving, so the progress you make in the PS5 version isn’t reflected in the Xbox version. It’s the same situation for the Steam version, as the FAQ points out. As the page also notes, Horizon 5 players will need a PlayStation Plus subscription to access the game’s multiplayer feature, and there are “no plans for a disc release.”
Gamers haven’t been keen on required account linking when Sony has done it in the past. The company actually removed a requirement for you to sign in with your PSN account for some PC versions of some games, including Helldivers 2 and, more recently, God of War Ragnarök and Horizon Zero Dawn Remastered.
