Batman was absent throughout the events of Ewan McGregor's Roman Sionis/Black Mask, which took place all throughout Gotham. Considering that it's his city, it's curious why Bruce Wayne was missing in action during this whole debacle.
Set some time after the events of David Ayer's Dinah Laurel Lance/Black Canary (Jurnee Smollett-Bett), Renee Montoya (Rosie Perez) and Cassandra Cain (Ella Jay Basco) — who also get tangled up with Black Mask and his hunt for a diamond. The precious crystal apparently has the key to the Bertinelli fortune, which the crime lord wants in order to expand his illegal operations in Gotham. For context, there was never any indication that Batman will factor in the film. Still, it's odd that this conflict plays out in his city and audiences hear nothing from him.
Harley and her team's struggle with Black Mask took them to varying parts of the city. At one point, almost all mercenaries in Gotham were rounded up by Sionis and ordered to go after the girls. Throughout this whole time, Batman wasn't in the picture. Harley did mention him a few times, however, and even named her pet Hyena after him, but other than that, the Bat of Gotham didn't have a presence in Birds of Prey.
All that being said, considering that Harley recapped her encounter with Wayne as seen in Suicide Squad, not to mention the fact that the film exists in the DCEU, it's safe to assume that the Batman she references is Ben Affleck's version of the character. Since the actor has long since exited the role, ing on the mantle of The Batman will also be in the DCEU.
In of narrative, assuming that Birds of Prey's Gotham has Affleck's Batman, it's clear that Justice League Part 2. There's a possibility that Yan simply followed the trajectory that Snyder set for his Batman. Since there's no clear future now for the franchise's original version, seeing as Reeves is more likely going for a reboot, there's really no ramifications for assuming that Batman is gone. If anything, this could help the franchise move on from the character. If this isn't the case, there's also the possibility that he's simply retired. Affleck's Batman was already old and beaten up — a unique approach on the hero who's typically depicted on the big screen during his heydays. Again, considering the time jump, Birds of Prey can get away with the idea that Wayne has already hung up his cowl and cape, and unfortunately, there's no one to take over the role as Gotham's protector yet.
Birds of Prey (And the Fantabulous Emancipation of One Harley Quinn) already set the stage for a potential Joker recast in the DCEU given the complicated status of Jared Leto in the franchise. While there was no official word regarding the whereabouts of Batman in the film, it did well still incorporating these characters to the story knowing that they have connections to Harley.
