Thought I should start a thread for this as this is anticipated to be significantly different from 2017 Theatrical version (aka, "Josstic League").
"Zack Snyder's Justice League, commonly referred to as the "Snyder Cut", is the upcoming director's cut of the 2017 American superhero film Justice League. It presents Justice League—the fifth film of the DC Extended Universe (DCEU) and based on the DC Comics superhero team of the same name—as director Zack Snyder had intended it before he left the production. Like the theatrical release, Zack Snyder's Justice League follows the Justice League: Batman (Ben Affleck), Superman (Henry Cavill), Wonder Woman (Gal Gadot), the Flash (Ezra Miller), Aquaman (Jason Momoa), and Cyborg (Ray Fisher)—as they attempt to save the world from the catastrophic threat of Steppenwolf (Ciarán Hinds) and his army of Parademons."
"There are many differences between the theatrical Justice League and Zack Snyder's Justice League. While the basic framework of the story is the same, dozens of additional scenes, backstories, mythos, worldbuilding elements, new characters, and teases for upcoming films are present in Snyder's version but not the theatrical release. Zack Snyder's Justice League will not include any scenes shot by Whedon for the theatrical cut, and former Warner Bros. executives Jon Berg and Geoff Johns—who oversaw the production of the theatrical release—chose not to retain credit for Snyder's version.
Snyder has stated that his version of Justice League will not be set in the same continuity as Whedon's version. Jason Momoa said that James Wan's Aquaman (2018) takes place after Zack Snyder's Justice League rather than Whedon's version. Similarly, Wonder Woman (2017) director Patty Jenkins said that no DC director considers Whedon's Justice League canonical, and that she had worked with Snyder to ensure Wonder Woman maintained continuity with his film.
Due to the length of the cut, Warner Bros. and Snyder decided to release Zack Snyder's Justice League [in March 2021] as a four-part series before combining the episodes into a four-hour film [on HBO Max]."
— From Wikipedia