I thought the multiverse as you describe it has been falsified, logically: if you could observe it then it’s part of our universe, therefore not a multiverse. If it cannot be observed, then it’s not a thing.

Perhaps that is just playing with the meaning of words or semantics to some, but it’s compelling enough for me.

The other description of quantum equations predicting many “worlds” I think is a different and more acceptable proposition. Like we’ve observed the shadow of an object, but can’t figure out how to observe the object directly.