I mean, gender expression is a social... cue... for lack of a better word. Gender roles are social constructs, but expression is more how you present yourself/how other people perceive your presentation.

Gender identity is all the internal feelings that match that (in the case of cis people) or don't match that (in the case of trans folks).

It's kind of literally the definition of being trans, like that's where the literal 'trans' or 'different' or 'crossed' or whatever translation you want to say comes from. Like, don't get me wrong-- someone is going to read what I say and say "wow this person is a freaking idiot." Great, do that.

Something else that I kind of want to touch on is the whole theory aspect of things. Straight up, I like theory, I like talking theory, listening, reading, whatever-- but (especially this sub at times) isn't always so friendly to theory and theorists and closer to "I feel therefore I am." (Don't get it twisted, that's cool too and I'm not firing shots or anything, it just is what it is, conversations here will be completely different than if you go to some scholarly trans/GSM group led by hipsters. That's all really long winded and I'm gonna get hate. I'm sorry).

I didn't read your article, but in terms of brain-sex, there are differences between sexes, but it isn't always indicative of gender. Ie- some cis girl's brain could have XYZ sized ABC regions, but a doctor neurologist doesn't toss an MRI scan on the table in front of her and gender her male from there on out. I'm sorry and also drunk.

I have no idea if this answers anything but I feel like I've typed too much to delete it all in frustration. Are you trans, OP?