Gender identity is social, not biological. From different pronouns and titles, different clothes for males and females, different hairstyles, different preferences for things that couldn’t have possibly existed when humans evolved, different perceived roles in society, etc. None of those are genetic, none of those you’re born with. So why can’t someone act how they want within that social framework, instead of how they “should” act based on a largely irrelevant biological factor? Transgender identity, similarly, is majority about acting like a different gender because you identify with what society has decided that gender acts like more.

In hunter gatherer societies for example, men and women did basically the exact same things in the tribe. Women hunted, men gathered, and vice versa. If that doesn’t bust the myth that modern societal gender roles have any sort of “biological” origin, I don’t know what does. More info with sources: https://yewtu.be/watch?v=VANvh-bA-BU