The label Gender Critical tends to refer exclusively to an objection/rejection of trans on every level, but as so often happens with trans-debate, it isn't that simple. All feminism is gender-critical by definition. The variance of that criticism doesn't have to go to the extremes of denying the concept of gender exists at all, nor does it have to go full-circle back to biological essentialism, and of arguing for or against women's rights on that basis. It's as complex an argument as the suggestion that all of us are to some degree non-binary. In which case, there'd be no need for fanfare when one of us 'comes out'.
No one can say with certainty to what extent our subjectivities are socially constructed, or where the line exists between constructivism and essentialism. It's a tilting at windmills debate. And if the nuture/social construct side of the equation is responsible for shaping our identities through a set of regulatory practices, embodied and encoded in historically-specific discourse as the likes of Foucault would claim, we can no more escape these constraints at any given moment in time than we can escape our biology.
Which is why it's so seriously concerning that things since the days of the new Romantics, Boy George, the second-wave feminists, the gender-bending of the likes of Bowie without exciting much comment, is such a retrograde (and in my view catastrophic) step. It starts at birth, and #pinkification. We must all be pigeonholed into neat little categories, and if those categories don't exist, they must be created so society doesn't have to face and confront its uncomfortable 'other'.
TRA et al are trying to boil this down to clear simplistics and brief soundbites. The creation of these categories are reinforcing and upholding the old, dangerous stereotypes (and the blue/pink unicorns/dinosaur binaries are as false and socially-created as any view of gender suggested above). The more we as a society subscribe to these, the more we'll perpetuate them. (And 'gender-neutral' clothing in babyhood is bollocks. There's no such thing as gendered colour-coding).
Pathologize everything, seems to be our motto. If it sneezes, waddles, quacks or squeaks, stick a label on it or diagnose something. If you're a woman and you're ageing, fill your face with botox; if you're a man and you cry or have depression, 'man up', talk to no one about your issues, and end up being one of the statistics of the biggest killer of UK males under 50.
We all suffer here. There are no winners. And no one has yet come up with a reasoned discussion as to what happens when the rights of two separate groups of people - women and transwomen - conflict. All you're likely to get out of that one is 'transwomen are women' and #NoDebate.
This Sam Smith, whoever they are, is doing nothing to resist such damaging stereotyping. They are perpetuating them.
Incidentally, I'm not sure whether the categories of 21 genders vary from place to place, but the one I've read contains the term 'cisgender'. It does not include 'male' or 'female'.