Exactly. It seems that some feminists think a woman is defined by her biology. I thought we fought against that? Well, I did. I'm older than a lot of you.
I remember suffering from this confusion about biological essentialism when I was a young woman (probably same age as you, at a guess) so I think I can answer you.
I am a woman, insofar as I have female reproductive biology. So far, so definitional.
However, it's a contingent fact about my identity as a person. I am first and foremost a person, who just happens to have female biology.
However, others have, historically and currently, weaponised this contingent fact about me to deny me and people like me rights. Having female reproductive biology is the marker societies use to spot one group of people they feel like shitting on from a great height. Therefore to try to strip away reference to my femaleness from the discussion strips me of the language I need to identify myself as a member of a group historically and currently shat upon politically.
Additionally, there are facets of my reproductive function which need to be taken into account in offering me equal access to society on a fair basis.
Take for e.g. the equal pay claim I fought a few years back. This didn't happen because my employer decided (evil capitalist cackle) to deliberately pay all those expressing a "feminine gender identity" less because... Instead, it was a classic case of cock up rather than conspiracy. Long pay scales, plus automatic annual marks of "doing okay" while on maternity leave, plus performance related pay meant that 10 years into the job, doing it just as efficiently as the man next to you, if you'd had a couple of periods of maternity leave, you'd be paid less than him.
Now of course one can argue about shared maternity/paternity leave as a route to fixing this, and I think that's a good one in an ideal society. But even then, it remains a fact that women need maternity leave in a way that men do not need paternity leave. Women need maternity leave because giving birth places a huge demand on a woman's body and she needs time to recover.
Biology.
It matters.
The trick is to recognise biology doesn't determine our worth as human beings, but does impact on our lives in ways that have to be taken into account if women (the sort of human being that produces the large immobile gametes, that gestates the young, that gives birth to them, that is capable of breast feeding them) are to be enabled to take a fair and equal role in society.