I haven't read Serrano yet (its on the list, but time is finite), but I've a bachelor in philosophy, and taken some classes on ontology. Ontology is awful, but studying it helps understand when someone is tuhinga to all you a load of bad goods.
Gender is not, in ontological terms, concrete. There are no particles or waveforms of gender. Its a different type of thing than a rock, or a plant, or a person. And if strict materialism is your benchmark for calling something real, you can say that gender isn't real.
Strict materialism is a pretty rubbish ontological standard, though. If we talked like we'd seriously committed ourselves to strict materialism, we'd be terminally pedantic and meaningful communication would collapse. We'd go around saying things like "Sherlock holmes doesn't smoke pipes because he doesn't exist and only things that exist can smoke pipes, even though the fiction says he smokes pipes." (The ontology of fiction is *hilarious*)
I think the reasonable ontological approach to gender is to recognise that it is a social and cultural convention which originated in humans applying their faculty for pattern recognition to the (incredibly complex, non binaristic) expression of human sexual chatacyeristics, developed through reason and rationalisation.
And like all psycho-socio-cultural cenventions, it's usable as a tool. Gender absolutely has been used as a tool for violence, repression and control.
But it doesn't have to be. Killers and chefs both use knives. Gender conventions can be a technology used for oppression, but it can also be a tool for building connection and positive identity.
I think of myself as agender. I'm normatively male by broad societal standards. I have a great big beard, a bigger bald spot and a beer gut. I have interests and behaviours that accord with some conceptions of msdculinity, But I don't have an internal conception of my own gender. I don't 'feel like' a man, i don't have a notion on what 'feeling like' a particular gender would be.
The certainty of trans women in asserting their internal conception of womanhood was what lead me to realise i don't have that type of internal conception. And I've seen of studies that correalate some neurological structures between cis and trans women, so there does seem to be some biological causation to trans identity.
But humans are conplicated! Biological sex expression is complicated enough, and humans have built a jenga tower of concepts and associations atop it.
We can look at an atom of carbon and define it's necessary and sufficient criteria, and demark the careful boundaries of the category.
We can't do that with any particular gender. There is no systematic, naturalistic criteria we can construct that captures a complete model of human gender that isn't arbitrary and simplistic. No physical test can be made without counterexample.
The thing that makes OP/Anon a woman is their earnest desire to conceive of herself as, and be considered ny others as, a woman. That's the only practical test of the concept: given the option, all other things being equal, what would you choose to be seen as.
When we acknowledge that gender is constructed, we can come to the understand that the associations and qualities are all of them provisional, and none are essential. It is a construction, and constructions can be renovated.
And lastly, I gotta stop wrting this at some point, but one last point.
You can accord with a standard or image that is enforced with violence without condoning that violence, and while fighting against that violence. The problem with the aesthetics and presentation of feminity is the violence with which it is policed (And the ways that the policing is informed by the male gaze, but afaict, the gaze is part and product of the policing and doubtlessly others can speak better on that topic than I)