What kind of computational model is the brain?
This is pretty much an open problem and subject to active research. There are a few proposals available. Here are some of the latest ones:

Brain computation by assemblies of neurons Christos H. Papadimitriou, Santosh S. Vempala, Daniel Mitropolsky, Michael Collins, Wolfgang Maass Proceedings of the National Academy of Sciences Jun 2020, 117 (25) 14464-14472; DOI: 10.1073/pnas.2001893117 [Link]

Manuel Blum's model of consciousness: [Video]