We do actually know pretty well how the brain works at the level of neurons. We don't know the higher levels of how all of those interactions work to produce certain behaviors.
Cellular neuroscience is a very active research field, and until we actually manage to derive organism behaviours from cellular-level models we won't know that those models are complete enough to do so. We haven't even managed that for C. Elegans, with 959 neurons, let alone humans, with 86 billion.
So we don’t know anything, we can mechanistically dissect any phenomena, but that rarely yields the ability to make interesting or useful predictions, i.e. understanding.
We don't even understand how a single neuron works and are still finding out they have way more connections and connection types than we thought they had.
I think it's safe to say we still have a woefully limited understanding of how the brain works.
And you don’t know how many “context tokens” the brain has. So don’t pretend