Microsoft confirmed this week that every non-Kinect title that works on Xbox One will run on Xbox Series X and Series S when those consoles arrive.
Meanwhile, Ubisoft says Assassin’s Creed Valhalla, Immortals Fenyx Rising, Riders Republic and Hyper Scape have full cross-progression support. When you play one of those games on one platform, you'll be able to continue where you left off on another. That'll be handy for Ubisoft+ subscribers.
Some backward compatible titles will have cross-progression support between the same console family: PS4 and PS5, and Xbox One and Series X/S. They are For Honor (which is getting graphics boosts on the new consoles), The Division 2, The Crew 2, Just Dance 2021 and Prince of Persia: The Sands of Time Remake.
Watch Dogs: Legion and Rainbow Six: Siege support cross-progression between generations too. Those two games are also eligible for free next-gen upgrades, as are Assassin’s Creed Valhalla, Immortals Fenyx Rising and Riders Republic. Additionally, Rainbow Six: Siege and For Honor support cross-play between console generations.