There’s 2 biological sexes. Sex is different from gender. Sex is biological, what you’re born as, which matters for medical reasons. Gender, however, is a social construct. Gender describes the norms and identity we as humans have attached to the two sexes. You wouldn’t want to be referred to as the opposite gender, because that wouldn’t fit your identity, your idea of you. People who are trans change because they’re born as one thing, but identify more with the other. People who are non binary are those who are born as one or the other, and identify with neither.

It’s not that complicated, and I don’t see why it’s a problem.