So your claim is that there are instructions, data, or both that are unable to be determined in what, is by definition, a fully deterministic machine?

By an individual person, yes. I claim that there exists no single human capable of fully understanding the totality of the software and hardware down to the individual transistor level.

That's a very wrong statement. Pretty sure I could explain all the maths, all the physics, all the electronics, all the operating systems and all the user space of a single high level language operation, when I was a fresh graduate. Now, I have forgotten most of the physics and electronics, since the university was quite some time ago, but feel free to ask any decent student of an IT bachelor, they should be able to pretty much build the PC from scratch. Sure, modern processors and whatnot add a bunch of optimizations, but you seem to really overstate the complexity of the computer.

We're talking about two separate things.

I'm talking about understanding, fully, the state of the CPU. Not just the conceptual operation of the CPU. Like, given a specific, modern AMD or Intel CPU, understand fully all states of all transistors.

I agree and never claimed that "a single person" could - but just because something is too complex for a single person to fully understand does not make it "mysterious" or a "black box". So what is the claim you are making? Anything beyond the complexity of a single person to understand = magic?

We're just using different definitions for "black box".

My definition is that it's something unknown, yours is that it's something unknowable.