Both PS4 pro and One X versions of the game has 4k resolution but in checkerboard rendering. Only improvement PS5 and Series X brings to the table is a stable 30 fps as the game has not been updated for current gen. Also One X version probably has better texture and shadow quality since that was the stronger hardware.

But

You can play first RDR on Series X and it's stable and beautiful, which is a big win.

Now if you'll excuse me I will go and apologize to my playstation collection