Translating what the multiverse is, so general audiences can comprehend it, will be the second biggest challenge for Marvel/Disney during these MCU phases. The first challenge will always be making the best quality product for audiences to spend money on.
There are extremely few pre-MCU movies that have dealt with multiple universes, realities, etc. The few that have are usually 1-to-1 in nature, mainly the protagonist exists in one universe/reality and travels or communicates with another universe/reality like The Cloverfield Paradox, Jumanji: Welcome to the Jungle, etc.
What Marvel/Disney is attempting is far more complex. I still think Spider-Man: No Way Home was a good introduction for general audiences but must honestly admit Dr. Strange and the Multiverse of Madness may have been "too much too soon" for some folks. Unfortunately, the multiverse theme is here and it will only grow in complexity in MCU movies and television series in my opinion.
I still have not seen Everything Everywhere All at Once yet. It has been marketed as a multiverse alternative concept to what Disney/Marvel is doing. It may explain things far better, albeit in a totally different story. One of these days I will catch the movie, probably on Prime Video I guess lol.