People believed and still believe in a lot of fictional things.
I'm not sure why you think "people believed in it" is an argument for the existence of anything. You're even calling it a myth yourself. You might look up the meaning of that word.
No, gender is a social construct, not a myth. That's like saying fashion is a myth.
You're making the most bizarre argument I have ever seen. People believed in Anubis for thousands of years. Please do show me one shred of evidence for the existence of Anubis as a real being.
I see, and you are claiming that all myths that lots of people have believed are true.
Therefore the myth of the intellectually inferior black race is true.
The myth of the inherently greedy Jew is true.
The myth of women being lesser beings than men is true.
The myth that war makes boys into men is true.
Oh, also the myth that you're born male or female and that's what you stay until you die? Also true based on your claim.
Drag didn't say it's true. Drag said it's not fictional. Fiction and truth are not a dichotomy. They're not even mutually exclusive. There's plenty of things that are both or neither.