“Biologically female” is kind of an ambiguous term. The way most people, (and you in this context) mean it is generally genitals. if you have x you are x if you have y you are y etc. This isn’t how it’s done in biology. Actually, the entire idea of being able to fit it into two boxes is itself flawed. The truth hates simplicity. There are people born with half of this and half of that, there are intersex people, there are people born with no genitals at all (By the way, intersex people are a lot more common than you expect - the percentages are about equal with the number of ginger people.) In biology, sex is classified as the size of your gametes (sex cells). If you have a lot of tiny gametes, those are called sperm and you are considered male. If you have a few small gametes, those are called eggs and you are considered female. It isn’t just that, though. There are plenty of species with more than 2 sizes of gametes, or only 1, or no gametes at all. Sex isn’t a binary, and any attempts to classify it as such almost always end up fruitless.