People do understand how quantum computing works. Quantum mechanics can fully explain what happens without invoking alternate universes.
But quantum mechanics is fundamentally different from our regular experience. And people like to grok things using analogies to regular experience. So that raises questions like, “How can the properties of an electron be random??”
That’s a nonsense question in quantum mechanics. They are random because they are random. Just like the charge of an electron is 1.6E-19 C because the charge of an electron is 1.6E-19 C.
Some people aren’t satisfied by knowing only the facts, so they come up with supernatural explanations. Like, “They only appear to be random, but they really aren’t because of alternate universes”. Which is equally unscientific as “The charge of an electron is 1.6E-19 C in this universe, but 900 in an alternate universe”. Which is equally unscientific as “God decides where the electron goes, and also decides its charge”.
They are all theories, without a shred of supporting evidence.
Therefore, I think it’s fair to say that if quantum computing becomes a real thing most currently used forms of encryption will immediately become garbage, because it can leverage the power of God to solve problems that are very difficult like factoring huge prime numbers extremely quickly.