Going forward, it will be Doctor Strange in the Multiverse of Madness which will introduce the concept of the Multiverse into the MCU.
So Marvel’s response to the challenge of coming up with a bigger threat involves redefining the MCU’s very concept of reality itself.
The Multiverse is a sci-fi concept that has been gaining greater popularity in pop culture in recent times, thanks to shows like Doctor Who and Rick and Morty.
The Multiverse has long been a part of Marvel comics, and various universes within the Marvel multiverse are shown to exist side by side, with different versions of the same heroes existing on their Earths in each of these realities.