Along with Birds of Prey, there was also a Gotham City Sirens film announced as well as a film focusing on the Joker and Harley.
Robbie herself has also talked about another project which, while she’s given little detail, appears to be yet another project that would include her character.
Margot Robbie’s Harley Quinn was far and away the biggest star coming out of the Suicide Squad movie and following that numerous projects were rumored or announced that would star the character.
Most of these projects have writers and/or directors attached, so they seem to be real, but when any of them would begin shooting, nevermind get released, was anybody’s guess.