I am mostly asking out of curiosity to know better our community's standards.
Joker (2019) is a movie by Todd Philipps with Joaquin Phoenix narrating the origin story of Batman's nemesis.
Are questions about this movie on-topic on scifi.stackexchange? Or should they be migrated to movies.stackexchange?
On the one hand, there are a lot of questions about the Joker on the site, steaming from various sources (comics, movies, video games,...) and isolating one movie seems odd. The character, a killer clown, has nothing fantastic or scifi-ish in essence, but his stories often involve scifi elements. It is definitely on-topic here.
On the other hand, the movie is very grounded in real life and, bar its name and a few references to Batman lore, the movie is completely disconnected from its counterpart in comics. Remove the names of Gotham and Wayne, it could have been the story of a man becoming psychotic in a Taxi Driveresque New York.
So far, there is only one question about the movie and it is about the trailer, so it was asked before we could know whether it has scifi features or not. Even after the movie was released, it is still fine since it asks about a characteristic of the character in the comics incarnation.