> No human can, or would, flush their entire brain to use every single neuron as working memory for chess.

We don't know what this means. Each neuron connects to thousands of synapses. I would assume that there is some quantity of information encoded in each pairwise connection of synapse-paths through a neuron. I would assume this is more than a bit, and also that it has something that might be described as a lossy fractal compression with each pathway adding or subtracting from whatever structures store information so that each path can use the same physical things - though not with perfect fidelity.

But the nuts and bolts are somewhat beside the point. The point is that if you look at Leela zero it only needs like 3GB of RAM to run and we have no evidence this is more memory than human grandmasters use to play chess. Yes, humans have imperfect recall but that's not relevant because neural net based chess engines do not work based on perfect recall.