No. Why should it be?
What makes you think that? The overwhelming majority of functions aren’t computable. The evidence suggests, if anything, that the universe is uncomputable and at best some isolatable well-measured specific phenomena can have approximations computed to some arbitrary but inexact precision.
Because if it's physically grounded then you can build a physical analogue of it.
> overwhelming majority of functions aren’t computable
By Turing machines, not by any other type of machine. As I said, if hypercomputers exist then they can solve the Halting problem, which Turing machines cannot.
Not only is there no practical way of creating such a thing, most formulations of physics preclude any possibility of making one by placing finite limits of the amount of space or time accessible to us.
(Not to mention that almost all reals are [Turing] uncomputable in their own right, but that's a more complex thing to demonstrate.)
I interpreted it to mean that we can predict the outcome of it, you interpret it to mean that we can model it.
Either way, maybe it doesn't matter since the original proposal is that consciousness is a subjective experience and there isn't an obvious way to define how to programmatically create it i.e. compute it.
And of course all TMs are just theoretical models. Non-deterministic Turing machine equivalents in particular don't physically exist and may be physically impossible.
But of course if there is indeed true randomness in nature that needs to be modelled, that same randomness can be used a source of true randomness for computation, and you can then build computation that does have stochastically determined results.