Deliberately not reading the thread so I can just post what I think!
I would say that confusions in this area come from confusions about the premise and purpose of the original question. So, caveat first.
If you say, 'what makes a woman,' you're implying something makes women women - that there is some process, which you could undergo, to construct a woman. I slightly worry about that implication, because it suggests that we have far more agency in the world than any of us do - whether you're looking at this from a hardline radfem perspective or a transactivist perspective. Realistically, however you define 'woman,' you still hit the hard wall of socially normalised, institutionalised misogyny, which will insist that, whatever a 'woman' is, she is to be controlled and undermined.
'Woman' as a noun is hugely culturally constructed: it is not simply a biological term denoting the presence of, say, vagina and ovaries or the absence of a penis. It is steeped in centuries of binary thinking and patriarchy, whereby it gathers layers of connotations to do with wombs and weakness and partnership with men. This is overlaid by libfem/wishy-washy attempts to reclaim 'woman' as a term of strength, by constructing largely bogus histories of women's special, spiritual and nurturing qualities.
However, 'woman' is also the term that has been used by feminists in order to allow people suffering biologically-based and gender-based oppression, to come together as a group, whose unification has real power. We live in a world where women are oppressed because they have the capacity to be raped, and to reproduce. The fact that some women are infertile, does not make a difference: we are all treated as the group that can be raped, and that can reproduce. This extends also to transmen and to lesbians, both groups who receive threats about corrective rape, which are intended to keep us within that group who can be raped, and reproduce. The same extends to some degree (and I know less about this) to transwomen, who are policed for failing to look enough like rapeable objects, and for looking too much like rapeable objects.
It is basic misogyny, and in this context 'woman' is the group of people who are aware that misogynists are targeting women on the basis of biology.
That's one issue. The other is gendered. We live in a society where, when you are born, the crucial categorising point is whether you have a recognisable vagina, or a recognisable penis. From this point, children and adults are presumed to have largely spurious differences, and this fiction of differences is used to oppress women. However, this gender issue comes back to biology in contexts such as pregnancy and labour: here, because gender (the social construction) has reinforced the spurious belief that women are weak, less able to cope with pain, and less sexually motivated, doctors are still encouraged to act as if birth trauma that impairs women's sexual function or causes them pain, is simply not very important.
The socially constructed aspect ('gender') and the biology it roots itself into, constantly interact. But it's worth noting that patriarchy isn't actually interested in accuracy about biology. If someone is infertile, lesbian, nonbinary, intersex ... patriarchy wants to put them in a box. And it says: this box is marked 'woman'. It means 'people who can be raped, and can reproduce'.
Because that generalisation is so damaging, we must be able to interrogate it, and show how false it is, and how completely it fails to justify the patriarchal idea of 'gender'. At times, that means you acknowledge that (for example) transmen were socialised as girls, and so have had some of the patriarchal assumptions about biology pushed at them. At times, you acknowledge that transwomen were socialised as boys, and so experienced the corresponding situation. You acknowledge that infertile women are generally treated as baby-making machines, despite the personal hurt this causes. You acknowledge that lesbians are seen, by the patriarchy, as potential sexual partners for men, even though this is an upsetting idea. You do this, because as we do this - recognising, for the moment, the category the patriarchy has put us into - we also find ways of showing how fraudulent and oppressive that category of 'woman' is.