Your link to the wikipedia article on the MWI does not clarify your objection to the statement made above.
The wikipedia article states
However, in 1985 David Deutsch published three related thought experiments which could test the theory vs the Copenhagen interpretation.[69] The experiments require macroscopic quantum state preparation and quantum erasure by a hypothetical quantum computer which is currently outside experimental possibility.
If a quantum computer could correctly be characterized as a computer which utilized the transistors in other branches of the multiverse to speed up calculations in this one, then it would merely require the operation o...
How many universes "branch off" from a "quantum event", and in how many of them is the cat dead vs alive, and what about non-50/50 scenarios, and please answer so that a physics dummy can maybe kind of understand?
(Is it just 1 with the live cat and 1 with the dead one?)