Men can't get pregnant. If a 'birthing person' gives birth, they are a woman. Trans men can be men, but they clearly aren't if they give birth to a child.
What is it about giving birth which meaningfully changes a person's gender?
What could be more quintessentially feminine than the experience of being pregnant & giving birth ?
As a transfeminine person, it breaks my heart that the feminine sacrality of that experience isn't available to me. However, reducing femininity to that is a dangerous antifeminist position that enforces the idea that people aren't anything more than their strict biological function. There's far more to feminine ideas and experiences than just being a baby factory.
You speak of "feminine sacrality" of the experience of pregnancy and birth while calling it "just being a baby factory" ?