It's not zero clue. Neurologists have got a lot of observations on how the brain works and there are multiple plausible proposed mechanisms for how the brain mi

It's not zero clue. Neurologists have got a lot of observations on how the brain works and there are multiple plausible proposed mechanisms for how the brain might do something like backpropagation, it's just that the details are really messy so there's not a single clear picture that has emerged. (Similarly, there is decent evidence that the brain uses higher-dimensional vector representations of concepts in a similar way to neural nets, at least in some parts of it, but again the details are messy and there's not a clear idea of how these representations emerge or how to decode them reliably)