Seeing this thread has given me a lot of insight on what it means to be non-binary. It's basically just internalized misogyny/misandry because you don't fit in with your sex's stereotype. There's a LOT more to it than that though.
It's interesting that most enbies are female. They don't actually want to be a man, but also don't want those socially constructed gender expectations of being a female shoved onto them either. I constantly hear about toxic masculinity, but what about toxic femininity? Pressured to look beautiful and sexy, to be dainty and cute, or to give birth and raise children. What if it's just toxic femininity that's making all these women resent being women? Girls are constantly worried what people think about them, this is why they flock to beauty magazines, starve themselves, and spend tons of money on make-up, hair and clothes, in order for society to accept them. When you give zero shits about this or don't meet these standards, but still feel pressured, it seems easier to just reject being "female" altogether and be something else. The opposite of this would be instead to fight it and support your sex, which is how the feminism movement started. I've met several females that use she/they pronouns who resent being female because they resent traditional female roles or hate their body because it's sexualized, and I have personally felt this way myself. Fortunately this thread has slapped some sense into me before I made the foolish mistake of going down the enby road and possibly butchering my body. I think we need to give tomboys more love and respect, because it's okay if you don't fit into the female stereotype, because there's lots of different kinds of women.