I can see why this idea would seem appealing to agender people. But that’s taking one’s personal case and turning it into a statement about gender as a whole. Gender having a biological component isn’t at odds with agender or NB people, but claiming gender is socially constructed is indeed problematic, like I said before.
To be clear, I’m saying gender identity isn’t a social construct (gender roles definitely are). And that’s hardly a radical statement given that there is a genetic factor to being trans, as evidenced by e.g. twin studies like this one which found a much higher amount of cases where both twins are trans among identical twins (who have the same genetic code) than non-identical twins. Also, like I mentioned before, a lot of trans people feel considerable relief to their own gender dysphoria upon seeking hormone therapy and gender-affirming surgeries, which is quite hard to explain on a social basis.