Differing from its rival PS5 in terms of backward compatibility, Xbox can run games without any special optimization. Witcher 3 ran on Xbox Series X and no console specific optimization was made. The loading speeds in the game are remarkable.
Fast travels in Witcher 3 happen instantly on Xbox Series X
YouTube user rubhen925 played Witcher 3 on Xbox Series X in a video he released. The game is backwards compatible, so it is not fully optimized for console. The user who shows us the game is using fast travel somewhere. Fast travel happens so fast that he has to wait a bit while the map is loaded. We can imagine how fast an optimized game can load with this video. In addition, the Xbox News twitter account shared a tweet regarding this situation. In the tweet, it was stated that fast travel on the Xbox Series X was fast even though Witcher 3 was not optimized.
— Xbox News (@_XboxNews) November 2, 2020