According to GamesBeat, Starfield is not coming for PS5 and will be exclusive to Xbox Series X/S and PC. Jeff Grubb also confirmed this with a short tweet.
Powered by the upgraded Bethesda Engine, Starfield was originally revealed at E3 2018. We don’t know much about the game yet, but it’s for sure that this whole Xbox exclusivity has something to do with Microsoft’s acquirement of Bethesda.
There were some questions about this going on since Microsoft acquired Bethesda, so there you have it: It will be an Xbox/PC exclusive. This might be just the beginning of Microsoft’s plan on Bethesda-made games, who knows.