In the 1950's Hugh Everett proposed the Many Worlds interpretation of quantum mechanics. It is so logical in hindsight but with a bias towards the classical world, experiments and measurements to guide their thinking, it's understandable why the founders of quantum theory didn't come up with it. Rather than proposing different dynamics for measurement, Everett suggests that measurement is something that happens naturally in the course of quantum particles interacting with each other. The conclusion is inescapable. There is nothing special about measurement, it is just the observer becoming entangled with a wave function in a superposition. Since one observer can experience only their own branch, it appears as if the other possibilities have disappeared but in reality there is no reason why they could not still exist and just fail to interact with the other branches. This is caused by environmental decoherence.It leads up to an interview of Sean M. Carroll, a many-worlds believer.
The concepts are explained pretty well, with good graphics.
Carroll tells that many-worlds allows essentially anything to happen, such as him being USA President or an NBA champion, as long as it does not violate conservation of energy or some other such principle. He says that this is not so strange, because we should ignore low probability events. Also, if you believe in an infinite universe with eternal inflation or some such mechanism, then there could be infinitely many copies of yourself doing bizarre things in distant galaxies/universes anyway.
Whilte the video exposes these silly arguments, it does not counter them.
Talking about infinite doppelgangers in infinite unobservable universes is no more scientific that discussion how many angels can dance on the head of a pin.
Carroll's use of probability was unchallenged, but the many-worlds theory has no way to say that any universe is more probable than any other. So while it is reasonable to ignore low probabilities, as Carroll says, there is nothing in the theory to say that those bizarro worlds have low probability.