No-one is arguing what "woman" means when you're talking just about biology.
Yes, they are. That's the whole point (well, one of them!)
Transactivist ideology says it's transphobic to talk about "biological women".
They insist that whether you're a woman on a man depends on who you identify. That if you have a penis but you ID as a woman, then you are a woman with a dick. (A "lady dick").
The trans activist line is that your sex is assigned by a doctor at birth, but it's only something you can actually know when the person is old enough to make their mind up about their gender identity. If that person was assigned male at birth, but now wishes to live as a woman, then all along, their body was biologically a female body. Just one that happens to have a dick.
Transactivists want to erase theuse of language that ties biology with sex.
e.g. they want us to stop saying that it's women who get pregnant. They say men can get pregnant too (i.e. transmen, who were women but now ID as male).
To stop saying periods are a woman's issues. To use the word "gestator" rather than pregnant woman, "chest feeding" instead of breastfeeding".
They say to use the phrase "female genital mutilation" is transphobic. To see a piece of information about the horrific practice of FGM and think - but what about trans issues - is a perfect demonstration of some of the narcissistic people who are attracted to this ideology.
They call lesbians who don't want to date transwomen (as they have penises!) transphobic, vagina fetishists, bigots.
Transactivists in Vancouver have been waging a battle for over a decade against a rape crisis centre / women's refuge, because they refuse to let transwomen work there as they want to provide a place for their clients that's penis free. (There are other refuges in Vancouver, all the rest let trans people in).
Transactivists want to literally erase the category of women as a separate group from male-bodied people who say they are women, in every area.