Sex in mammals, defined by the function of producing sperm and ova, is indeed binary. No serious biologist will disagree with that. I don't really understand the problem with that.
If there are 10 people in a room, and 9 of them have brown hair and 1 of them has red hair, you cannot assert "There are no people with red hair in this room.".
The "Exceptions don't count!" argument amounts to nothing but grasping at straws to deliberately make your parameters for defining these words exclusionary.
You have no reason to deny the validity of these "exceptions" that disprove your absolutist definitions, so why do you?
Lmao there's several animals capable of changing their gender. There's plenty of animals with a sexual dimorphism that goes beyond just "male and female" showing a wider range of what we can understand the concept of "gender" to be. If we go on to include bugs and molluscs shit gets really wild. Don't get me started on fungi