There are virtually no coherent arguments. Which is why discussions with the activists typically don't go anywhere. They aren't concerned with understanding the phenomenon they simply wish to further what they already believe to be unfalsifiably true. It's like a creationist at a science conference, it's perfectly fine to posit the theory that life is designed by a higher intelligence, but the creationist isn't saying , here's a theory of mine that fits the evidence I see, they're instead interpreting the evidence to fit into what they already know to be true and cannot be convinced of otherwise. So evidence that doesn't fit will be disguarded or attacked as false and irrelevant evidence that seems to suggest they are right will be given a huge focus. It's a make the facts fit the theory approach rather than making a theory to fit the facts approach. It's a common human failing. All too rampant in many different ways. The recent trans movement falls into this same pattern.

They aren't dropping the brain argument because there was never an argument there to be had in the first place, they're only interested in converting you into their cult or attacking and demonizing you if you cannot be converted. They'll simply move back and forth and create novel arguments and theories as quickly as they can and move onto the new ones before anyone can establish their legitamacy through more rigorous debate or experiment.

The other problem comes down to what is essentially sociopathic behavior.

They also bought up non binary and claimed you can be a girly girl, dress like a girl but not feel like a girl and feel more comfortable seeing yourself and being perceived as non binary.(TBH i've never seen a NB like this

I will fully agree that "non-binary" exists in this manner. You can be, anyone, do anything possible, and not "feel" like you are that which you are. I simply say that your self perception is useless to everyone else and a meaningless concept when it comes to describing what you are. A fireman that feels like a police officer means what? Exactly? A fireman isn't defined by the uniform, or the name, but by what they do, put out fires. A fireman could certainly dress like a Catholic nun and still be a fireman. Although we'd certainly point out such a concept would be silly because catholics don't wear fire protection during mass, it wouldn't at all change that the concept of "fireman" is defined by what a person does, not what they think.

Likewise a woman is not defined by how one feels. I don't know any useful way to describe what being a woman, or a man, or a human, feels like. I only know what I feel like. It's meaningless for me to try to grasp what part of my existence feels like me because I am a man or a human or whatever, I can't be something else I can only speculate. We are all simply ourselves and have no experience being anything other than ourselves.

What I can say though is that there are two clearly distinct categories of human from a functionally reproductive standpoint. There's no way to argue against that. You have three options in humans. Ability to impregnate. Ability to be impregnated. And infertile. And that's it. An infertile man is still a man, just as an infertile woman is still a woman, since we recognize it as a disability and not a separate category of human. Someone born without legs is not a new species. They are simply a human born without legs.

Intersex conditions certainly create some vague edge cases but the current arguments aren't really about them. I don't think any women really care about someone born with an intersex condition who is for all intents and purposes a woman in appearance but cannot get pregnant and technically has male chromosomes, using women's facilities. But again there are edge cases and we should be at the very least considerate of these and have legal options available for legal sex changes on documents and the like. There are situations that arise where it can be reasonable and fair to do so. It is however quite rate and not at all related to the typical transexual experience or current social issue.

As for whether or not the brain is structured differently? Hormones and certain other sexual differences do create some statistical average differences between the sexes. Male brains are expectedly bigger than female brains. Males are larger than females in general though.

Of course some males are smaller than some females so you can't simply look at two brains and make an accurate judgement on what gender the brains are.

The main reasons why the brain argument isn't relevant to the current cultural discussions around this though is simply because brain scans aren't used to diagnose gender disphoria. And can't be used because we have no clue how it works up there.

I'm all for having the discussion and research done on the brain to see if there are sexual differences and if that might be a correlation between that and sexuality. But I don't think society is necessarily ready to accept the findings of that. Anything that might indicate that men and or women are better than the other is not politically viable and such research would be suppressed. For example while I don't at all prescribe to this idea that all women are stupid. As there are many very intelligent women much smarter than me out there. But I do think that if you took the entire population and averaged everything out you'd find that women are more "average" than men. And that men are more extreme, in both directions. Extremely intelligent, and extremely stupid. Now how much of this is culturally influenced and how much is due to biological reasons is another debate that I don't think can ever truly be determined exactly.