Gender is factually, as evidenced via a multitude of highly respected scientific studies conducted by a vast majority of respected experts both medical and psychological, distinct in every way from biological sex.
There is genuinely no room for opinion, disagreement, or dispute on that subject, at all. To disagree is to be, objectively, incorrect.
I can see where you are coming from in a purely politically motivated sense, yes. But the medical and psychological facts do not actually care about politics, and transgender individuals exist regardless of your belief in them.