https://www.gamespot.com/articles/red-dead-redemption-2-file-size-revealed/1100-6462541/

Red Dead Redemption 2 is big and bright, deep in the heart of Texas. Following an apparent look at the game size for PS4 Pro, the full file size on Xbox One has been revealed as well. The "Additional Information" section on the Microsoft Store lists its approximate size at 88.57 GB.

Weighing in at nearly 90 gigs puts it close to the leak from the PS4 Pro Bundle, which suggested it would be 105 GB. It's possible that the disparity can be chalked up to the Pro version downloading some extra textures, and that it would be similarly sized on Xbox One X.