DC Comics recently released The Riddler: Year One, a comic book written by The Batman star Paul Dano that details the villain's descent into insanity.
In that, a woman is shown holding a train ticket that will take her to Metropolis. This isn't the first time we've had confirmation the city exists in Matt Reeves' Bat-Verse, as a child's book, Batman: An Original Movie Novel, revealed that a character called Dex also hailed from Superman's home and was a member of the LexCorp Race Team.
No additional details about the city are revealed in this comic book, but as Reeves had input into this story, it's fair to say Metropolis definitely exists in this specific DC Universe. Now, that doesn't necessarily mean Superman is out there, and we anticipate this franchise remaining standalone.
After all, James Gunn and Peter Safran's DC Studios is in the midst of creating a brand new DCU that will bring together the Justice League, and the former has already confirmed Robert Pattinson's Dark Knight won't be part of those plans.
Rather than having Batman cross paths with his fellow heroes, Reeves instead seems far more interested in adding new villains to his Gotham City. A Penguin TV series is already in the works for HBO Max, while we've heard rumblings about plans for The Joker, Clayface, and more on the streaming platform (though whether those will happen given the changes being made is unclear).
Ultimately, this is little more than an Easter Egg and probably not something to get too excited about. Reeves only really started delving into Gotham City in The Batman, and we'd bet on the sequel remaining there rather than heading to any other familiar locations from the wider DC Comics Universe.
Take a closer look at that panel from The Riddler: Year One below.