Batman v Superman, the middle child between Snyder's Man of Steel and Justice League, released with a theatrical cut that snipped away lots of scenes many fans would consider important to creating a cohesive narrative, despite arguably being overstuffed. The decision to replace this DC Comics film with the Ultimate Edition was announced by HBO Max on Instagram yesterday, which said it is a good way to, "Put that long weekend to good use."
Originally, Batman v Superman and other movies were going to be removed from HBO Max on July 1, but after backlash from fans Warner Bros. extended their availability through December. There are also DC Comics television series in the works for the platform, including one based on Green Lantern, and it seems the 2019 Harley Quinn cartoon will also be coming to the service.
It's fair to say the availability of these shows and movies can be somewhat confusing given there is also a DC Comics-specific streaming service called DC Universe that hosts its own original content. For instance, despite the first season only appearing on DC Universe, the second season of Doom Patrol has also recently begun airing on HBO Max.
Batman v Superman: Dawn of Justice is available now on HBO Max.