The "weirdness" of QM all stems from a belief in "value indefiniteness," which is the idea that particles have no real properties when you are not looking at them, but suddenly acquire real properties when you look. If you believe that, then the question naturally arises, at what point do they acquire real properties precisely? What does "look" even rigorously mean? This issue was first brought up by John Bell in his article "Against 'Measurement'". The "answers" to this always fall into one of three categories:

1. "Look" just means you become aware of it. This devolves into solipsism, because other people are also made up of particles, so they would have no real properties either until you become aware of them.
2. "Look" is more of a specific physical process that measuring devices do. But this is vague without rigorously and mathematically defining what this physical process is, and if you do define it, then it's provable that no definition can be consistent with the mathematics of quantum mechanics. If we agree with the premise that "quantum mechanics is correct," then such an approach is trivially ruled out.
3. There is no "look," systems never acquire real, observable properties at all. But then you run into Wittgenstein's rule-following problem. If the mathematical model never predicts that a system acquires real properties, then you can never tie it back to any real-world observation.

The "weirdness" stems from starting with an assumption that is not logically possible to make consistent in the first place and then developing dozens of "interpretations" trying to make it consistent, but none of the major interpretations are ultimately logically consistent if we agree that (1) objective reality exists and (2) quantum mechanics is correct (some may be argued to be consistent but only because they openly admit they're dropping off #1 or #2).

Feynman's belief in "value indefiniteness" stems from an argument he made here regarding the double-slit argument and how probabilities should add together. I made a video here explaining why his argument does not work, but you can also read John Bell's paper here because von Neumann made a similar flawed argument and Bell gave a similar rebuttal to it.

If you just drop off "value indefiniteness" as an assumption, which has no justification for it in the academic literature, then all the quantum woo around quantum mechanics disappears, and the arguments over interpretations like Copenhagen or Many Worlds or QBism simply become superfluous.

I can do (some of) the maths, but I definitely can't explain why any of it is like that, or how it works.

Plain stupid