Believe in the existence of sex is evidence based. Belief in the existence of gender isn't.
Knowledge of gender is evidence based, we know that we gender clothes, names, pronouns and loads of other things. There is nothing innately biological about calling girls Kate and boys Kevin, that's a social construct.
What we have no proof for, is how much of gender or gendered behaviour is taught and how much is innate.
As an old lesbian, I know loads of other old lesbians many of whom have had children via assisted conception, which overwhelming, leads to male children. Some have done their absolute best to raise their boy in as gender free an environment as they can.
One is particular was quite a committed second wave feminist, her boys were taught to pee sitting down, had an array of colourful, non gender specific clothes, were give dolls, not toy guns etc, were encouraged to feel and share their emotions. All of the stuff that we thought would cure gendered behaviour.
She didn't raise them in a lab, the did socialise but they didn't have television and didn't spend much time around adult men.
By about four, they were pulling the arms of their beautiful dolls to use as pretend guns to shoot each other and taking great delight in peeing standing up. They are nice young men but they don't stand out as being particularly sensitive or unsullied by gendered behaviour.
Of course, this is an anecdote about a single family, it's not 'evidence' of anything. We don't raise children in laboratories because that would be cruel, we can't establish what's outside influence and what comes from within.