With stuff like transgender and genderfluid I do. I don't believe in the demigirl non-binary xe pronoun stuff but even then I will call someone who identifies as such what they want me to call them.
It's weird. As a mtf this is a question that lingers in my head. It's like: what MAKES me and other trans people identify as the opposite gender? Is it because of gender roles?
At the end of the day I say I do believe in it because I don't think I'm trans due to gender roles such as being girly (liking women's clothing, heels, makeup, pink things, etc). But it is complicated.
Yes. I do believe that gender and sex are not the same. I know for a lot of people, it's easy for them to believe otherwise because they were born with a gender that matched their sex, and couldn't imagine anyone feeling differently.