there is no evidence of back-propagation in the brain.
See Professor Edmund T. Rolls books on biologically plausible neural networks:
"Brain Computations: What and How" (2020) https://www.amazon.com/gp/product/0198871104
"Cerebral Cortex: Principles of Operation" (2018) https://www.oxcns.org/b12text.html
"Neural Networks and Brain Function" (1997) https://www.oxcns.org/b3_text.html