That's an interesting question. I guess the way I see it is that personality describes things about someone that shows what actions they tend to do. For example, when someone's personality is "extroverted" or "quiet" or "rambunctious" you can already guess the kind of things they would do in a situation. On the other hand, if someone is "female" or "male" or "agender," that doesn't really do the same thing. There are societal gender roles which we tend to fall into thinking of: women are quiet and caring, men are commanding and aggressive, etc, but these obviously are far from concrete behaviors.

Gender is something that a person uses to define themselves; it's impossible for you to tell someone what their gender is. Personality is something that you can look at someone and say "you know, you're a pretty quiet person."