"Superman: Legacy" is written and directed by Gunn (Gunn directed 2021's "The Suicide Squad" as well as the "Guardians of the Galaxy" series for Marvel). The movie is not an origin story of Superman, aka Clark Kent, but will deal with how he balances being from Kypton with being raised by humans. In June, it was announced that David Corenswet and Rachel Brosnahan will play Superman and Lois Lane.
There's also another Superman movie, written by Ta-Nehisi Coates, in development, but it won't be a DCU film. "Superman: Legacy" is the only DCU film with a release date and will hit cinemas in 2025.