Right. A person's gender is what they say it is, because they ultimately know themself best

Sorry, but you can't just change someone's gender, and that's a fact

https://medicine.yale.edu/news-article/what-do-we-mean-by-sex-and-gender/

When you say "science" who or what are you referring to specifically?

You know what, my argument (that since you listed them all in one place, that they were mutually exclusive) was stupid, but either way, I'll repeat what I said before: facts don't care about your feelings