sex based rights
Not sure I am in a position to explain this as it was something said to me (when I used the phrase gender critical).
Part of the problem is the campaign to blur the lines of the meaning of the words sex and gender means you cant assume someone takes the same meaning as you do when using either or both words.
Yes being gender critical could be just about not wanting gender stereotyping to happen from the moment of birth by family, school, advertising, etc., etc..
Sex based rights is about the basic underlying reality of discrimination against women just because of their sex. The gender stereotyping is one of the mechanisms, but sex discrimination is not just about being made to wear pink, but the fact that male violence against women happens irrespective of whether women are performing the gender stereotypes that society (ie patriarchy) imposes on us.
It maybe that there should be two parallel campaigns to help get this across to those who aren't particularly aware or focused on who things are drifting.
ie get rid of gender as a concept in the same way as people challenged racist stereotypes
and campaign against sex discrimination in all areas of life, work, home, male violence, sexual exploitation
(Obviously more complex than this but posting in haste.)