It's indeed confirmed that the Snyder Cut of Justice League is a part of a DC Multiverse and is no longer attached to DCEU continuity.
Zack Snyder actually talked about the notion last week when he confirmed the existence of a DC Multiverse of movies, and now during this weekend's JusticeCon which saw footage of the Black Superman suit revealed, it's reported Zack said his Snyder Cut is considered an "Elseworld's" film, which is a reference to the DC Comics Elseworld storylines involving alternate takes on the characters set in alternate universes.
The info comes from Sean O'Connell, the Managing Director for Cinema Blend, who is writing a book on the Snyder Cut and its movement:
.@Sean_OConnell revealed during his #JusticeCon panel that Zack Snyder referred to his Justice League film as an “Elseworld” film and is not tied to the current DCEU continuity pic.twitter.com/sJGxdAf4xk— Geek Vibes Nation (@GeekVibesNation) July 26, 2020
Snyder Cut part of DC Multiverse not a bad thing
Regarding what Zack Snyder said last week about the DC Multiverse of movies, he basically confirmed his flicks are separate and no longer tied to the DC films, which as he notes, isn't a bad thing:
"For me where the movie falls, I believe it starts to represent its own path. It's kind of separate now from where I would say the DC Cinematic Universe in continuity. I think it's divergent in that way. I think that is a good thing. You know the power of DC and one of its cool strengths is the Multiverse concept."
Why it can be looked at as a good thing is that the DC movies will continue on in theaters, while Zack can continue his own vision on the HBO Max streaming service, which is where the Snyder Cut is getting released next year. It's also rumored that Zack Snyder will be continuing his "SnyderVerse" on HBO Max with additional Justice League projects and possibly even Ben Affleck back as Batman.
Years ago prior to releasing Man of Steel, Zack Snyder actually said his version of Superman was going to be its own thing and separate from the Justice League, so the notion of "Elseworlds" in the movies isn't something entirely new. To boot, Michael Keaton is also rumored to return as Batman, so who knows? Maybe there could be an epic Crisis On Infinite Earths movie down the road.