If reality is finitely complex, how does it get to have no bottom?

What does it mean for reality to be finitely complex? At some point you not just need to become able to predict everything, you need to become sure in your predictions, and that I consider an incorrect thing to do at any point. Therefore, complexity of reality, as people perceive it is never going to run out (I'm not sure, but it looks this way).

Surely things like the double-slit experiment have some explanation, and that explanation is some kind of QM, and we're forced to compare these different kinds of QM.

Quantum mechanics is valid predictive math. The extent to which interpretation of this math in terms of human intuitions about worlds is adequate is tricky. For example, it's hard to intuitively tell a difference between another person in the same world and another person described by a different MWI world: should these patterns be of equal moral worth? How should we know, how can we trust intuition on this, without technical understanding of morality? Intuitions break down even for our almost-ancestral-environment situations.

Vladimir_Nesov's post is regarding where we should look for morally-relevant conceptions of reality. He is advocating building out our morality starting from human-scale physics, which is well-approximated by one-world classical mechanics.