You won’t find a reputable gender and sexuality therapist, psychologist, or psychiatrist that will deny that difference.
Some of you may not know the specifics behind the differences, so just for clarity’s sake, here are one liners pulled from Wikipedia:
Gender refers to the socially constructed roles, behaviors, activities, and attributes that a given society considers appropriate for men and women.
Sex refers to the biological and physiological characteristics that define men and women.
Gender and sex are, simply put, not the same thing.
Except for the 98% of the population whose sex and gender are the same. For them, there is no difference between gender and sex. As someone who has never experienced a disconnect between the two, it’s hard to grasp.
On Earth, mass and weight are functionally the same. In my day-to-day life, I see no reason to recognize the difference.
Does my experience of a total match-up between mass and weight discredit the scientific finding that the two are different?
Absolutely not. My lack of expertise is irrelevant. A difference exists, whether I chose to acknowledge it on a daily basis or not.
The distinction between mass and weight may only matter if you are in the context of a technical or scientific sphere, but by that logic the distinction between gender and sex only matters if you are in the context of people who experience gender dysphoria. And when you talk to me, a girl with a trans boyfriend, it is an extremely relevant distinction.
Just because we haven’t experienced the difference between two things, doesn’t mean that a difference doesn’t exist.