Neural networks were modeled after a model of the neurons in human brains, a model which we know by now is inaccurate and misses a lot of details.

So, that's pretty wrong.

Spiking neural networks are possibly closer to being biologically analogies, but they kind of suck to train and don't have good performance.

It takes a lot of computer "neurons" to simulate a single human neuron, and we can't simulate it perfectly in any case.

Well, yeah, that’s why it’s a model. Our weather models can’t predict the weather perfectly either.

How does the brain do backprop?

Airplane wings and tails bear about as much resemblance to bird wings and tails as neural networks do to neurons.

The way airplanes fly doesn't even vaguely resemble how birds fly. Same with neural networks and brains.