What is the flaw of biological frameworks for sexuality?

One of the biological frameworks is gender essentialism which bases the gender of an individual on biology. The flaw to this framework is that not all individuals can be categorized as either female or male based on their biological features alone. Human biology is not perfect and some are born with two sex organs. "Sex change" is also now possible by removing and replacing reproductive organs. With these, it becomes difficult to determine the sexuality of an individual.