sex is just biological, born a male or female ( or if nature did something weird to you )
I think gender involves a lot of self expression. There is the traditionally held man/woman thing, and each culture has varying expectations on it. For example like a century ago, the red/blue color association flopped, and young boys were in dresses because they were easier to potty train that way. And then you go back further and men were wearing ruffles and heels ( at some point that jumped ship to women's side, weird )
The easiest thing to do is play the norm. Most people accept their given gender without fuss, or just don't give much thought or importance to it.
Some people feel very strongly about realizing deeply held convictions about themself and having other people validate it.
To me I feel like gender is a personal experience, you decide what is true about yourself. I don't feel the need to inform anyone what my thoughts are about myself or be validated / called by special names. For example I'll get a chuckle out of people assuming I'm something else; I don't care if they are wrong about what I am, it is just interesting to see how others perceive you and they are usually trying to be respectful whatever the case. I don't require any tip-toeing. I am not usually interested in other's thoughts on their gender especially if I just met them
People who do require pronouns and validation, to be honest I have a bad memory with names and faces and then throwing pronouns in there I'm going to mess up and it's not intentional. If somebody sets up strict social rules about how to interact with them I will probably avoid them just because I don't want to set off any tripwires. However if it's somebody I come to like and respect I will remember anything about them, like their favorite movies and foods and so on