It could well be the case that the brain can be simulated, but presently we don't know exactly what variables/components must be simulated. Does ongoing neuroplasticity for example need to be a component of simulation? Is there some as of yet unknown causal mechanisms or interactions that may be essential?

None of those examples cannot be done on pen and paper or otherwise simulated with a different medium, though.

AFAICT, your comment above would need some mechanism that is physically impossible and incalculable to make the argument, and then somehow have that happen in a human brain despite being physically impossible and incalculable.