Though he still hasn't confirmed which project it was, James Gunn has shared more details on the DCU movie that was scrapped despite having a script and director

Director Richard Donner’s Superman: The Movie, which premiered in 1978, is a classic piece of cinema that continues to shape the superhero genre today. Most recently, it led the way for writer-director James Gunn to release Superman, a more modern imagining of the Man of Steel’s adventures, with David Corenswet portraying the titular hero.