90% of people only perceive others as either men or women.

That sounds ridiculously high. Where's that study from, Prager U? 😛

Even if they see a nonbinary person, their occipital lobe would still generate a man schema or a woman schema

That's a learned bias though, not an inherent state of the occipital lobe or any other part of the brain.

Are you gonna use that as evidence that binary gender is objectively real, because billions of people wouldn't hallucinate it

Nope. I'm gonna use that as an example of learned bias and other outside influences can affect how we experience the world in a very literal sense. In fact, I just did. Twice.

Cause that's the same argument you're making now.

Nope, not at all. Please stow away all strawmen before proceeding.

And it's not an empirical argument.

It is and it isn't: paradoxically, it's impossibly to establish the existence of objective reality with 100% certainty.

That being said, what IS possible is logically deducing a conclusion so overwhelmingly likely that there's no valid counterargument.

To give you an example: the only way to know without a doubt that the sun is hot is to touch it yourself. Given that it's impossible to get to it and touch it, we rely on more indirect measuring which are still reliable to the point that no well-informed and rational person doubts that the sun is indeed very, very hot.

That's how both logic and science works: in the absence of the possibility to positively prove or disprove something, you rely on what's most likely.

To elaborate: You have absolutely no empirical evidence to back up your claim that homo sapiens don't suffer consistent illusions. And you never will. It's entirely vibes based metaphysics. And even so, we do have empirical evidence that homo sapiens do suffer consistent illusions, and your vibes are wrong. "The chance is astronomically remote" how did you calculate that? Did you go check our perceptions against a magic crystal ball? Or did you check them against themselves, which is a tautological and unscientific endeavour?

As I alluded above, belief in veridical perception directly harms nonbinary people. And other groups too. You're sitting in an armchair and speculating over metaphysics that you'll never be able to confirm, while your misconceptions hurt people. Belief in objective reality that aligns with perception is a religion as made up and as harmful as christianity.