Biological gender is impossible to deny: if you have an X and a Y chromosome, you are male; if you have two X chromosomes you are female. Most of us reach some accommodation with this. However, through the vagaries and variations of biology, some human brains may be constructed to feel fundamentally at odds with their own gender. That might be just the way they are. It’s not a large proportion of the population. A 2011 survey by the Equality and Human Rights Commission, classified 1.4% of the UK population as being of “a gender minority group”, according to wiki. (I assume the percentage is now higher, but still a small minority.)
Such a state must be an affliction, and its sufferers should be supported in their efforts to come to terms with it.
We do not need to redefine gender to do this. Within these broadest of categories, everyone should be free to live as they choose, as long as it doesn’t damage others. If a man wishes to live as a woman, even have a sex-change, be referred to as “she” that choice should be respected. We should be helping them to minimise the distress their gender is causing them.
If we aim for an inclusive society that accepts and celebrates the individual and their autonomy, rather than creating new genders, we should be reducing, not increasing, classifications and labelling. These are the impersonal tools of those who would limit and control us: governments, marketing agencies, the social media giants. And labels are the laziest form of identity-formation.
We should protect the indeterminate, the personal and the independent, accepting people just as themselves.