Zack Snyder's Justice League is very much the face of the DC Extended Universe, and if nothing else, is the entry with the most momentum and fan support. A close second behind the HBO Max exclusive is Black Adam, which will bring the protector of Kahndaq to the big screen.
This film has next to no narrative ties to what Snyder introduced in any of his three movies, but this might actually work in it and the DCEU's favor. Black Adam seems to be a sort of rebirth for the franchise and could take the universe in an entirely new direction away from the previous controversial entries.
Black Adam and the Justice Society
One element that's been known for some time is that Black Adam would introduce the Justice Society, but it wasn't clear how many members would be present. This is similar to how Batman v Superman introduced early members of the Justice League, but with one exception. For one, Black Adam actually has ties to the JSA in the comics, making their appearance in his film more organic. It's obvious with their presence, however, that Warner Bros. has much bigger plans for the team.
The Rock is perhaps the biggest name to be featured in a DCEU film yet, and his being the protagonist of Black Adam will help to make it an easy sell. In this way, Black Adam could become the new headliner of the DCEU, with the Justice Society being branched out as "Phase 2's" Justice League. This matches with the pre-release headline for the film, which claims " the hierarchy of power in the DC Universe is about to change." It's obvious from this alone that Warner Bros. is far more interested in developing this section of the cinematic universe than anything Snyder laid out.
WB's recent statements also back this up, with the Snyder Cut's massive success seemingly doing little to persuade them otherwise. While loyal fans of the Snyderverse have demanded its restoration, there's no question that his direction for DC's classic characters has been decidedly controversial. Actually following up on his plans for an apocalyptic Justice League sequel featuring an evil, Injustice-inspired Superman would likely only throw salt in the wound. Thus, moving away from these characters outside of solo films and focusing on the comparatively unknown Justice Society might be better for right now.
The Power of Shazam!
The one DCEU flick Black Adam is destined to be connected with is Shazam! Black Adam is right behind Dr. Sivana as the arch-enemy of DC's Captain Marvel, a trait which has stuck around even with that character's massive reimagining in the New 52. While the second Shazam! is telling its own story before Teth-Adam's film is released, the third entry will likely feature the World's Mightiest Mortal facing off against his predecessor.
Shazam! followed in the footsteps of 2018's Aquaman by going in a much lighter direction than what Snyder had planned out for the DC movies. The film was generally well-received, and the more childish tone fit the character without feeling generic or like the movie was trying to emulate the MCU formula. While Black Adam will likely be a good bit more serious, having ties to something so largely opposite of the Snyderverse's tone will likely only help the film in the long run. This all depends, of course, on the movie actually doing well, as its failure could cause the pendulum to swing back. As of now, however, the movie has a lot going for it, and it seems that a villain will ironically pave the way for a better and brighter DCEU.