ok so this topic is iffy. Now let me make some things clear. When people say that gender is a social construct they are talking abt the concepts of maculinity and feminity. Gender identity is rooted in your brain. Trans people have the brains of their cis counterparts. Trans men (female to male) were born in a female body but their brain is male and vice versa for trans women. Now for non binary people, not much research was shown so we dont know for sure. The reason people say "gender is a social construct" to validate trans identities, isnt to say how they are trans but why they transition. Being trans isnt a choice but wanting to transition is. You see, trans people have something called gender dyphoria, which is when the brain feels like it is in the wrong body. The only way to change this is to medically and surgically transition to give the body the secondary sex characteristics that matches their brain. However, in modern society, we have made these triadic or third sex characteristics called gender expression, aka masculinity and femininity. For the longest time, men were to me masc and women were to be fem but now we challenged these notions because gender expression is a social construct. So trans people dont necessarily have to follow every single stereotype of their percieved gender if they dont want to. Now for nb people, they may also feel dysphoria but only half of it or insecurity in different places. It isnt confirmed for them but we should be respectful towards their pronouns because it is a decent thing to do.