Physics has reached a point where many things aren’t directly measurable. If we create a theory that explains everything in the observable universe and requires a multiverse, some scientists would accept that we may never know everything. Others might continue exploring different possibilities, refusing to accept those limits.
Most people would agree that it would be ideal to have a theory of the universe that’s self-consistent, covers everything, and doesn’t rely on things we can’t observe. But that might not be possible.
Some researchers argue that if something can’t be tested in the usual scientific ways, it isn’t real science, it’s pseudoscience. For you, the question is whether the goal of science is to discover the truth about the universe, or just to focus on things that can be proven through experiments.