Does The Batman crossover with Joker? Matt Reeves says that was never the plan

gamesradar.com:

The Batman and Joker have a lot in common. They both put darker spins on classic DC characters, feature versions of Gotham that are grounded in reality, and even have similar plot points (though we won't touch on those here). However, there was never a conversation about the two being in the same shared universe.

Despite every other film studio aping to copy the Marvel formula and have heroes and villains appear in each others' movies, Warner Bros. decided to let directors Matt Reeves and Todd Phillips tell completely individual stories. That's not to say The Batman and Joker won't lead to more stories of their own (there are already multiple Batman spin-offs in the works) but there was never any intention to have Robert Pattinson's hero face Phoenix's Clown Prince of Crime. 

In fact, while Reeves was writing The Batman, he did not know Joker was being developed. "I was finishing the Planet of the Apes movies when I first came on board, in 2017. It's been five years in the making," he tells Total Film in an extended interview. "When I was working on the script, and got deep into the script, Joker hadn't come out yet. I didn't know what Joker was or what it was going to be." 

"I became aware of it once we were very deep into the film, and the fact that they were grounding things in a way that was reminiscent of things that we were doing, that wasn't planned," he continues. "Joker was always meant to be a very specific standalone that Joaquin [Phoenix], and Todd [Phillips] were doing. There was never really any discussion of crossover."

However, Reeves saw how hungry audiences were to see a more grounded Gotham. That had, he says, always been the goal of his Batman movie, and the reception to Joker simply bolstered his