Note: Contains Spoiler for Spider-Man: Far From Home .
According to the time travel games of Avengers: Endgame the possibility for a multiverse was established in the MCU (with colliding alternative realities, as in the unconnected, animated Spider-Man: are explored).  The second trailer for Spider-Man: Far From Home seemed to confirm the official arrival of the multiverse, with Nick Fury (Samuel L. Jackson) declaring Quentin Beck, AKA Mysterio (Jake Gyllenhaal), come from the earth, "just not from us".
We know Mysterio from the comics. Is the multiverse really in the MCU? We are about to seriously ruin so swing out of here if you have not Far From Home yet.
Well, first of all, Mysterio (not surprisingly) is a big liar. Beck is an angry former employee of Tony Stark who is responsible for the holographic technology that led to BARF. This was demonstrated in Captain America: Civil War (1
With his holographic technology, Beck created the Elementals and deployed weapon-protected drones – by William Ginter Riva (Peter Billingsley, who reiterates his role as Iron Man ) – to bring about a real destruction in the Beck saving the day each time that completely excludes the multiverse in the MCU?
It is interesting that Beck describes the multiverse of Earth-833 and the main MCU Earth is Earth-616. This is part of the cover story written by one of Beck's team, Guterman (Nicholas Gleaves), for their Elementals List.
Both, however, are actual realities in the comics, so if Marvel wants to bring out the comic version of the multiverse In the MCU, they would have to find a way to explain how the hell Guterman knew these numbers.
Perhaps during his work at Stark Industries, he came across some of Dr. Erik Selvig and gave this Guterman. A Thor: The Dark World Easter egg had Selvig write "616 Universe" on his blackboard, so that Guterman was inspired here.