At my workplace, we are now completing the multiscale simulation of a full mouse brain (neuron/synaptic activity, cellular metabolism, etc). It fits into our small supercomputer first deployed in 2019, and there's a large potential for simplification not yet realized.
I believe that a supercomputer from the top 5 can already simulate a human brain. But we don't have the data and the theory yet. We are developing it, though.
Are you talking about real time or faster simulation of complete cellular metabolism incl. neural activity across an entire mouse brain? If not, then I'd say I can run a simulation like this on my home computer. It will just take forever to compute something meaningful. But if yes, that is insanely impressive, even though this won't scale to the human brain any time soon since it has 1000x more neurons and exponentially more synapses.
I believe that a supercomputer from the top 5 can already simulate a human brain. But we don't have the data and the theory yet. We are developing it, though.