We are all limited by our biology in a variety of ways. My digestive biology makes it impossible for me to survive on a diet of bamboo. My respiratory biology makes it impossible for me to breathe water like a fish. My skeletal biology precludes me from growing a pair of wings. All the self-determination in the world can't change these biological facts. Why should my reproductive biology be the only exception? My reproductive biology means I can only be a mother, never a father. My husband's reproductive biology means he can't contribute to breast-feeding our child.
The point you are missing is The Patriarchy was using biology to justify the discrimination of women just like biology is being used to discriminate against trans people. It's effectively saying there was no psychological legitimacy to women or trans people being treated equally because of their biology when there clearly is.
Self-determination never meant that we could re-write biology to suit our preferences.
Biology isn't being rewritten for trans no more than it was rewritten for women. The justification for self determination was psychological interchangeability. Both women & trans people have been accused of lacking legitimacy in these areas.
There's a reason why MRA blame feminism for the increased visibility of trans gender people because they believe feminism opened the door to their legitimacy when they claimed interchangeability with men…& they would be partly right.
What it means is that, when it comes to the choices we are all free to make - such as what work we will do, or what hobbies we will pursue, or who we will love, or where we will live, or what clothes we will wear, or how we will vote - our sex should not dictate the options available to us.
Yes & trans people have been discriminated is similar ways in terms of access to employment, housing, health care public utilities, safety etc. Like women protections from discrimination have been written into law & like women inequalities still persist on many levels despite the law.