Here's what had happened: Snyder and his wife Deborah lost their daughter Autumn to suicide during the filming of Justice League, so Warner Bros. granted him a leave, during which time Whedon was hired to sort of finish the film. That's what we got when it debuted in theaters a few years ago, but many fans -- me included -- felt like Whedon had, either intentionally or unintentionally, turned the film into too much of a comedy-riddled corny mess; you can definitely feel where the Marvel-esque tone of his Avengers crept into the dialoguing, and while I didn't mind the theatrical cut (I don't think it was nearly as bad as critics made it out to be -- as I felt about Batman v Superman and Wonder Woman 84), Snyder's version is definitely a bleaker, darker and more serious take. Even Steppenwolf comes across as more threatening and brooding, while Superman's handling of him during the final fight sequence is more satisfying and "real."
