Essentialism - the reliance on Plato's concept of essences to specify categories like genders - is the core problem here. The problem with such essences is that identifying the necessary and sufficient characteristics of a category is near-impossible for any non-trivial (ie. more complex than an geometric shape in normal [Cartesian] space) example.
If you have a category, Cat, you want it to have the necessary and sufficient characteristics to include all cats that ever have been, all cats that are, and all cats that will be. But the problem is if you say cats are furry, you exclude sphinxes and cats that have lost their fur; if you say cats have tails, you exclude cats that have had traumatic tail injuries and Manx cats. And did you intend to include lions and tigers in what you meant by Cat?
This is the problem of categories: the more the characteristics (and their specificity), the fewer members that the category will contain; conversely, the few the characteristics, the more members. Every time a property of Cat is added, fewer creatures are considered to be a cat.
The same is true for pretty much anything else. Every time a characteristic is added to the Essence of Woman, or Man, the more people are excluded from it. Famously, this results in women assigned female at birth being excluded from the category, but it could also include people assigned male at birth whose genitals don't match their genetics. In terms of the Essence of Man, we're told that gay men should be excluded from being considered men because we don't behave in the right way.
Relying on essences hurts everybody, including those that the categorisers set out to protect.
The only way to reliably consider categories is to look at the Becoming. Cats undergo biological, social and behavioural developmental stages ("progressive differentiation") from conception which undergo patterns very similar to but distinct from dogs and humans. The progressive differentiation of women and men have huge overlaps in terms of biological, social and psychological development, but there are distinctions, and what's interesting is that often trans women have more in common with cis women than with cis men (for example, there's some suggestions that neurological structures in trans women are more similar to cis women, there's also evidence suggesting that trans women internalise misogyny very early on).
We are all Becoming, we're all changing, we're all adapting to the world in which we live and the experiences, traumas and interactions which we're constantly engaged with. Suggesting that we can be reduced to an unchanging essence denies the reality we can see with our eyes. It's long been suggested that genders are something we become as a result of our journeys from the moment of conception to the moment of death (and even then discoveries can be made post-mortem).
So focussing on essence, particularly to the point of "gender essentialism" defining one's own identity, makes no sense. The becoming is far more interesting than the theoretical being projected onto us by other people.
