It's wild how consistently "nonbinary" gets treated as just a spicier flavour of transmasculinity, and not a range of identities both transfeminine and transmasculine people both hold. Within trans online spaces, transfemininity is seen as almost anathema to being nonbinary.
It's like, either you're a feminine cis man who is still cis, like a femboy, or cross-dresser, or you're a binary transgender woman 'gender conformist' who has an absolutely uncomplicated relationship to her gender. There's no in-between, and any sign that a transgender woman might have a more complicated relationship to her gender is grounds to exile her to the former category of femboy or cross-dresser.
Being nonbinary is only socially permissible in transgender spaces when you're transmasculine, because transfemininity is subjected to such intense scrutiny that that anything short of swearing an oath of undying loyalty to Artemis that you will forever and exclusively be a woman is grounds to treat you as a male cross-dresser.
You can see this in a lot "androgynous" fashion styles as well, especially in what bodies get to be counted as androgynous. Typically, the bodies are white, thin, and (stereotypically) feminine, save for the absence of boobs, while the clothing is (stereotypically) masculine. The fact that this is an idealization of transmasculinity is not an accident, and it makes transfeminine nonbinary people hoping to be socially read as such extremely difficult.
The only alternative for them is the 'man in dresses' stereotype, which not only reduces them to the status of a cross-dresser, but which is constantly fetishized and repackaged as "gender fuckery" by TME people who think it's exotic. And I know some transfem nonbinary people get a lot out of this, I know a few of them, but for the vast majority of us, it's a complete misrepresentation of how we actually want to present.
These fashion and body standards are not the cause of this pattern so much as the shared effect of the pervasive transmisogyny directed against transfemininity which constructed transfemininity and nonbinary identity as anathema to begin with.
This anathema is typically employed against transfeminists as well. I am nonbinary, and yet I could not tell you the massive stream of people accusing me of being a binary trans woman who denies the existence of nonbinary people and who do not believe me when I try to explain otherwise.
When people say transfeminism is "exorsexist", what they mean is that they can't understand transfeminine people as nonbinary, that they refuse to recognize our identities, or to understand our experiences.
Either we're cross-dressers, or gender conformists. Either we're men, or anti-feminists. Transfems are denied a gender identity.