Gender critical is what feminists are, from the get-go. One of the reasons, presumably, why they were quick to spot the writing on the wall with regards to trans ideology.
The ideology relies on sexist stereotypes in order to exist. If a man identifying as a woman isn't relating to the actual sex of the women, i.e. gametes, childbirth, uterus, then what makes him think he is one?
It's the way women think, or behave. When in reality, no two women think or behave the same.
He's relying on stereotypes. And often highly sexist ones, at that. You don't tend to see these men shouldering the childcare, looking after elderly parents and cleaning the toilets.
We had a transwoman on here a few years ago who said they only felt they could be 'vibrant' when dressed as a woman.
The ideology upholds strict gender roles. Cements them in. Hence gender critical.
That doesn't stop almost the entire rest of the world understanding that humans can't change sex, hence sex realism.