*Cue amateur philosophical musings*
To me all this just makes it seem more logical to talk about "brain sex" and "body sex" and that "gender" is just a thing society makes up to assign people with roles. Given there's fairly significant evidence at this point that male and female brains do have differences and that those differences logically exist along some kind of spectrum, I think it makes perfect sense that one could have a "female" brain inside a male body, or vice versa. Actually considering there *is* a spectrum, it's probably not even accurate to talk about brains in terms of them being "male" and "female" but rather to just use those things to identify the poles of the spectrum. Makes me wonder if there *is* some kind of "brain sex scale" roughly analogous to the Kinsey scale. My instinctive hunch is that there is, but people don't like this because it's not neatly binary. I don't see why sex should neatly fit into a binary breakdown when pretty much nothing else we know about the nature of mankind does. Anyway, so for these purposes:
"Body sex" has a fairly set definition with some rare exceptions - what chromosomes have you got? The answer to this question also seems to be largely irrelevant outside of discussions about a person's physical health or reproduction.
"Brain sex" is much harder to identify anatomically, but the simplest way to find out is probably just to ask people "what sex do you think/feel that you have?" much as the best way to find out where people fall on the Kinsey scale is just to ask them.
Both of these seem like highly innate (probably genetic or at least determined largely by prenatal environmental conditions) characteristics to me that don't seem to have much to do with gender. If they did you could get a transperson to change their "brain sex" just by forcing them to adhere to gender roles that society aligns with their "body sex," but we already know this doesn't work.
To me there's clearly a difference between whatever this "brain sex" sense of identity that 99% of people have and "gender" - which I just consider to be a bunch of fairly arbitrary rules society made up based on a very limited understanding of "brain sex" and its correlation with "body sex." It's about the best cavemen can manage to help police and legislate behavioral tendencies when they have no understanding of psychology or neuroscience.
Sorry if people don't like my terminology. I just made it up on the spot and was trying to use words that were precise and understandable. Also, I'm really not trying to make any point here. This is literally just me thinking aloud (or in type as it were).