Joaquin Phoenix might be interested in making a Joker sequel
Emphasis on the "might."

Could Joaquin Phoenix be back as Joker?
The new film Joker has made plenty of headlines and a lot of cash, so normally, Hollywood would be already buzzing about a sequel. There hasn't been that kind of fuss about a Joker follow-up, but now star Joaquin Phoenix sounds like he might be open to the idea.
"I talked to (director) Todd (Phillips) a lot about what else we might be able to do, in general, just working together, but also specifically, if there's something else with Joker that might be interesting," Phoenix said in an interview for Popcorn with Peter Travers.
That's intriguing, but don't plan on anything just yet. When Travers noted that Phoenix "doesn't do sequels," Phoenix pondered the idea, saying. "I don't know that there is (more to do)."
And Phoenix isn't dreaming of his character sharing screen time with Joker's nemesis, Batman, saying it hasn't been his dream to act with the Caped Crusader.
But the actor said he enjoyed the Joker role so much that "me and Todd would still be shooting now if we could, right? Because it seemed endless, the possibilities of where we can go with the character."
Back in September, Phillips said there were "no plans" for a sequel. But that was before the film enjoyed the largest October domestic opening weekend ever, so who knows?