I came across this video trying to understand what are quantum computers about... After all, Feynman himself said: "If you think you understand quantum mechanic

I came across this video trying to understand what are quantum computers about... After all, Feynman himself said: "If you think you understand quantum mechanics then you don't understand quantum mechanics." and "If you cannot build it, you do not understand it." I wonder if anyone could link to something that makes the stuff clear. https://www.youtube.com/watch?v=dKAF9OCQtIo https://www.youtube.com/watch?v=dKAF9OCQtIo "QBism is NOT NEW but at least people are reviving what Bohr thought. QM just involves expectations of observables and the Born rule is just "metaphysical fluff." The confusions are all about false counterfactuals."