While comic book movies are still the most popular thing in the world, despite there being a significant lack of movies, there's still really been nothing quite like Joker. The movie really took the concept and character of the clown prince of crime from the comics, but then built a world around him that was unique to say the least. It was a box office smash and it was nominated for 11 Oscars, and went home with two. It's not exactly shocking that there was talk of a sequel despite the fact that it was difficult to see where the story would go from there. And while the project had fallen off the radar, assumed into oblivion, there's some evidence that a Joker 2 might still be in the works.
A recent story from THR delves into many different corners of the DC universe on the big screen including how the currently filming Flash movie will give creatives access to the multiverse. But it also makes it clear that of all DC film and TV projects so far, there are only four that don't take place within the same universe. Two of them are Robert Pattinson's The Batman and it's associated series Gotham PD, and the other two are Joker and its "planned sequel."
The fact that a sequel to Joker is even being referenced would seem to indicate that the movie is still very much an active concern, but the word used here is "planned" and not "potential" or even "anticipated." The word choice seems to indicate not only that the idea of Joker 2 still exists, but there is, at least right now, still a plan to make the movie a reality.
On paper, you would expect that to be the case. You don't have a movie as popular and successful as Joker and then not look at how you can keep that going. And there were reports following the first movie's success that a sequel film could happen. But back at the end of 2019 director Todd Philips said that, while there had been unofficial conversations about the idea, there were no deals in place to make it happen.
Of course, even if there is a planned sequel to Joker, it doesn't mean that Joaquin Phoenix or Todd Philips will be returning. Although, you have to assume that is the hope. The bigger question, however, has to simply be how it would work. Even Todd Philips has admitted that Joker was only ever planned to be one movie and it's not really designed to have a sequel. At the same time, neither Phoenix nor Philips have ever completely discounted the idea of making a sequel either. If somebody has found a way to make another movie that could be as powerful as the first one, maybe we'll see it.
We'll have to keep an eye on this one. As of now there is at least some evidence that there are people who want to make Joker 2 happen. Whether or not it really will is another question entirely.