Zack Snyder's Justice League is one of those strange projects where it's kind of unreal that it's really happening. The theatrical version of the movie was a legendary dud at the box office, critically, and more importantly, with the fans. Director Zack Snyder needed to step away from the production of Justice League for an entirely justified reason, and Warner Bros. brought on Joss Whedon to do some reshoots and finish post-production work. At the time, it was seen as a mutual decision for everyone involved, but within the last three years, there have been more and more rumors and allegations that it wasn't that mutual of a decision. Those allegations are still being put through the investigation process at the time of writing.
When Justice League came out, fans began to notice the difference between the first Snyder-directed trailer and the theatrical version, and thus the myth of the Snyder Cut was born. The Snyder Cut, a mostly finished version of Justice League before the finished post-production and reshoots, existed somewhere, and it just needed to be released. They campaigned hard for the release of this cut. Eventually, HBO Max announced their intentions to release Zack Snyder's Justice League, a mini-series that would require an additional $30+ million to complete. The existence of Zack Snyder's Justice League is proof that the mythical, mostly complete version of the Snyder Cut did not exist. Interestingly, Warner Bros. and HBO Max are willing to put the budget of many smaller-scale movies into something that underperformed at the box office and initially went overbudget. It means they have a lot of faith that this project will bring in a lot of new subscribers to HBO Max.
Snyder is, at the time of writing, breaking down the new black and white version of the trailer for Zack Snyder's Justice League over on Vero. He also released that black and white version of the trailer on his Twitter.
— Zack Snyder (@ZackSnyder) November 17, 2020
Zack Snyder's Justice League will stream to HBO Max sometime in 2021.