Xbox Series X box art for Far Cry 6 shows that it’s actually just box art, with games that support Smart Delivery listing both Xbox One and Xbox Series X. Moreover, games that are Optimised for Xbox Series X will display a (rather large) label heralding the feature.
You can take a look at the Far Cry 6 box art above, which sports a green bar with “Xbox” at the very top, followed by a black bar with available platforms. All up, it looks a lot like Xbox One box art of old, just like PS5 box art is pretty similar to that seen for PS4.
Far Cry 6 heads to Windows PC via Uplay & Epic Games Store, Xbox One, Xbox Series X, PS4, PS5 and Stadia where available on 18 February 2021.