Starfield will let you play on both Xbox and PC with only 1 version of the game
"Play Anywhere" is Xbox's in-house program that means you buy the game on Xbox Series X/S, you can also play it on PC (and cloud) and vice-versa with your saves transfering between versions, meaning you can play some of the game on one platform and then hop over to the other and start from the same spot.
Also, all of your Achievements & DLC's will automatically be shared between both versions.
