Every single person saying "sex is real, it's gender that's not real" to support trans people needs to sit down and think about how that affects intersex people.
Sex is literally made up. Sex characteristics? Real. Genitalia is real, hormone levels are real, chromosomes are real... But dividing those into two boxes isn't real. We arbitrarily threw together the two most common combinations of these traits, called them male and female, and said fuck everyone who doesn't fit into that.
Sex isn't some holy thing that only the most radical people want to destroy, it's a farce used to justify the medical abuse of intersex people. If you want to be an ally to intersex people, please take the time to think about these things. Think about the way we talk about sex and how it might be hurting intersex people.
Using "assigned gender" language, legitimating the idea of a sex binary, calling intersex types "conditions"/"disorders"/etc., comparing intersex people to animals with diverse sex characteristics, and not listening to or acknowledging intersex people are all things people need to stop doing if they want to be allies to intersex people.
I'm trans as well as intersex, I know that supporting trans rights is incredibly important, but it should not be done at the expense of intersex people.