The main reason I think consciousness is just advanced firing of synapses in the brain is because drugs can impact it, surgeries can impact it, flaws in the system can impact it.
If it was anything more than physical, these things wouldn’t affect consciousness so easily.
Take those who have had their Corpus Callosum split. It’s widely viewed that patients with this procedure end up with two distinct consciousnesses communicating with each other (www.ncbi.nlm.nih.gov/pmc/articles/PMC7305066/) which suggests to me that consciousness must be nothing more than the effects of complex physical systems in our brains.