I'm not sure what people really mean by 'non-binary' - how does it differ in practice from being 'gender critical'?
Hm, in feminist activism practice, non-binaries support transactivism, so that'd be the difference there.
"Gender critical" is not an identity, it is an opinion. I can be gender critical and be a very much "feminine" appearing person, because that is how I happen to be. Being gender critical just means applying critical thinking to gender stereotypes.
"Non-binary" would, in theory, seem to require a pretty much androgynous appearance, style, hobbies, etc., to look plausible to the onlooker.
In fact, though, I think "non-binary" it is just a way out for those who aren't comfortable with conforming to gender stereotypes, but have swallowed the koolaid of genderism. It is applying a label to onself: "I do not want to be forced into either stereotype category, but I still worship the stereotypes, please don't hate me! I am a weird exception! Gender is real!"
While a gender critical feminist would say "Yeah, I have short hair and don't shave my legs, and I am a woman, because biology. That's what the facts are." Or even "Yes, I do all this work to conform to patriarchal beauty ideals, but that is not what makes me a woman, having female sex organs is what makes me a woman."