Yes, you were incorrect in several points.
Sex-based oppression isn't real. That's not how oppression works. People oppress one another based on identity. The kind of oppression a trans man faces is not the same as what a cis woman faces, because the cis woman doesn't experience the transphobia the trans man experiences, and the trans man can be impacted by misogyny but isn't targeted by it the way a cis woman is.
All trans women and most transfems are women and female, so it would make sense to say that they're included in your original statement. People wanted to call that out explicitly, but you then clarified that you think trans women and most transfems don't count as women or female, which is incorrect.
AFAB does not mean biologically female. It only means one thing, that the person in question was assigned female at birth, by a doctor assuming they were female based on the shape of their genitals.
AFAB isn't a term originally created by and for the intersex community. The original term was 'coercively assigned male at birth' and it was coined by trans women. After being adopted by the rest of the trans community, it was also shared with the intersex community and is a celebrated point of commonality between all of us.
Biological sex is a social construct that doesn't describe the biological reality of humans. Being born with a penis doesn't make you biologically male and being born with a vagina doesn't make you biologically female. Those ideas are just prevalent because most people are cis men or cis women and their gender and sex traits all line up in a typical pattern. Biological sex is a social construct that isn't based on biological reality, because it doesn't account for trans people or intersex people.
You can prove the previous by looking at how people will discard anyone who doesn't fit their preconceived notion of biological sex, in order to justify their need to deny that a trans person is the gender they say they are. See: People who claim any woman who can't give birth isn't a real woman, that people only have XX or XY chromosomes, that intersex variation doesn't matter, etc.
If you're talking about actual biological fact, trans women are biologically female because our gender is female and we just happen to have other sex traits that are not typical for biologically female people. Same goes for trans men, who are biologically male, because they have a male gender with some atypical sex traits, and intersex people as well, who can be cis or trans and have atypical sex traits.
Something that's important to understand about trans people in particular is that we are the gender we say we are. The only real difference is that our bodies came out shaped a little different than what you expect. It's not a mental condition, we are just rare examples of what men, women, and non-binary people look like in the human population.
Many people who are transphobic or gender critical or whatever kind of name they're giving to their prejudice these days think that trans people merely 'think' we are the gender we say we are. These people think that we're wrong and that we're either mentally ill or are literally evil.
In reality, we are the gender we say we are, and these kinds of people just hate us because we look different from them. This is the exact same kind of attitude you find in proud racists who believe that anyone who isn't white is a lesser form of human, and in some cases, not human at all. People hating other people because of how they look, not some actual true thing.
When you argue that women are not actually women because they don't meet your definition of female, that's misogyny talking.
When the women you're talking about are intersex, that is intersexism because you're denying that they're biologically female because they may have been born with TAIS and have testes instead of ovaries.
When the women you're talking about are trans, that's transmisogyny because you're arguing that trans women are biologically male and thus are not Actual Real Women.
And finally, when you argue that trans men are female, you're engaging in transphobia by denying that they're Actual Real Men. You may feel a sense of solidarity with someone who the doctor also claimed was a girl at birth, but if he's not a woman you are doing him a great disservice by acting like he is one.
You should respect the reality of human biology and not try to act as the arbiter of who counts as a man or a woman, male or female.
