A neuron fires, or it doesn't. The patterns received by neurons via synapses are binary. The synapses themselves are analog, and the activation can trigger in several ways, leading to complex behavior, but the signal each individual neuron receives from any and every other neuron in the brain is digital.
Where an impulse comes from, when it is sent, the current charge state of the receiving neuron, the specific neurotransmitters released by the axons, and the efficiency of signal transmission at a given point in time all play a part in the signal sent along dendritic, but at any given point in time a neuron is firing or isn't, and that's the only state that matters to the other neurons it's connected to.
The biggest difference between biological brains and artificial neural networks is the analog nature of biological timing compared to the arbitrary cycles of software.
Spike timing dependent plasticity networks address some of the problem of variable timing and its impact on signaling.
https://en.wikipedia.org/wiki/Spike-timing-dependent_plastic...
At any given moment, you could capture the state of a biological brain as a binary number. The model would need to account for all sorts of analog mechanisms and a huge, biologically messy graph of connections with dozens of variations across a handful of neuron types, and the length of a synapse and where it physically connects or touches other synapses without connecting directly and... lots of stuff that's hard to model and even hard to see.
I'm not arguing that every part is digital or even equivalent to computers on silicon, simply that the basic mechanism of computation is itself digital pattern processing. It literally cannot be anything else.
There is no evidence or theory to indicate any other plausible method of operation. All the analog stuff can be swapped out with an arbitrary bit length representation and the functionality is retained. Remove the digital assumption and everything breaks. You need magic or spirit to make it work, which is ridiculous because silicon computers proved that binary computation is a perfectly fine way to represent and process data. Quantum processing in biological brains is magical thinking performed in a desperate attempt to ascribe eminence to human cognition, because for some reason people don't like the idea that brains do digital processing.
We are messy and vastly complex and sophisticated digital pattern processors. Which makes evolutionary sense, because that's how our predecessors work, all the way back to single cell organisms and self replicating DNA chemistry.
Signals and patterns in the real world can be represented as binary to an arbitrary precision. The Planck length dictates the maximum level of precision relevant to our universe.
https://www.researchgate.net/post/How-many-bits-of-informati...
Human brains achieved a special state of depth and breadth of processing, concurrent with physically encoded, evolved algorithms in our neural architecture. The arrival of biology at human cognition affords us the privilege of deep reflection, the apparent subjective reality we experience, and the thus far unlimited scope of conception such that we can make approximations about the size of the universe or the mass of a photon. Or the operations of the minds we possess.
We operate in binary - the explanation is sufficient, simple, and corresponds to all known evidence. There aren't any outstanding questions requiring that premise to be questioned.