Rocksteady hasn't released a game since 2015 (not counting Batman: Arkham VR), when it delivered Batman: Arkham Knight, the final game in its Batman: Arkham trilogy. However, not only has the UK studio not released a proper game since then, it hasn't revealed one either. In the face of this though has been numerous rumors and reports over the years on what it's working on. Most of this scuttlebutt has pointed to a new Superman or Injustice game. Meanwhile, there's been a suggestion here or there that it could be developing a Suicide Squad game. For now, it looks like it will be one of the former two, but only time will tell.
That said, a new rumor has surfaced that seems to claim there's a Batman or Justice League game coming exclusively to Xbox Series X. The rumor comes way of NeoGAF user OsirisBlack, a leaker with a mostly reliable history of scoops, though the scoops in question are admittedly a bit vague and noncommittal. More specifically, when asked about third-party console exclusives Microsoft have nagged for the Xbox Series X, they responded with a few teasers, including this video, which as you can see is a pretty big hint at a Superman Xbox Series X console exclusive game, or at least a timed console exclusive.
Again, the NeoGAF user in question has a mostly reliable history of leaks, and is cited by many as a credible leaker. That said, all of this should still be taken with a massive grain of salt given that it's somewhat vague, but mostly because it's unofficial. Until you have official confirmation, it's best not to give too much credence to any single leak.
That said, if Microsoft does have an exclusive Superman for Xbox Series X that would be a massive get, and something I imagine cost them a pretty penny. In fact, I'm not sure why Warner Bros. Interactive Entertainment would even contemplate the idea -- as it's not something it's really done in the past -- unless Microsoft threw an absurd amount of money at the publisher, which is possible. After all, Microsoft does have a massive war chest.