This is in the same sense that while it is technically correct to describe all physically instantiated computer programs, and by extension all AI, as being in the set of "things which are just Markov chains", it comes with a massive cost that may or may not be physically realisable within this universe.
Rainfall to the exact number of molecules is computable. Just hard. A quantum simulation of every protein folding and every electron energy level of every atom inside every cell of your brain on a classical computer is computable, in the Church-Turing sense, just with an exponential slowdown.
The busy beaver function, however, is actually un-computable.
