Gotham Knights might let you play with up to four players online, despite so far being advertised as allowing two-player co-op.
At the moment Gotham Knights is only meant to let you play with one other friend online, but the PSN store page for the game has recently been updated to say that it "supports up to 4 online players with PS Plus" (via Reddit). It reiterates this point by differentiating between support for offline and online maximum number of players, with offline only allowing one, and online allowing four. So far, in all the marketing for the game, only two-player co-op has been advertised, making this a bit of a big change for online gameplay.
Gotham Knights was originally meant to launch last year, after being announced in 2020, but saw a vague delay into 2022. However, the game now has a confirmed release date of October 25. The delay into 2022 was confirmed in March of 2021, so it's almost a year and half long delay, meaning the increase to four-player co-op could be a big part of the delay.
It's unclear how that might change online gameplay, as missions are designed around two-player co-op, but it could also be a mistake on the store page. We do know that while the game is separate from the Arkham games, it is taking a lot of inspiration from it mechanically, but combat has been designed around the fact it features online co-op.
Though if you did think Gotham Knights was a follow-up to Arkham Knight, it would be perfectly understandable, considering the latter ends with Batman dying, and the former's main concept being about Batman dying and his crew of traumatised kids looking after Gotham.
But this is also the first game that focuses on the Bat's sidekicks, so there's big questions over whether people will even care as much without the big guy. Though with Gotham Knights being the first adaptation of The Court of Owls storyline, it should offer something a bit different for fans of the caped crusader.