I think some people like promote a kind of binary - people who are 100% happy with the constraints of their gender role in our society and those that are not. The first group is almost everyone and they are boring and non special while the second groups is a tiny chosen few who get to be angry at the first group all the time.
Of course it’s nonsense. Many many people don’t enjoy aspects of the little box they are supposed to Live in. It’s not just your son OP.
Does he think that you dress, live and act exactly as you would wish all the time ? I’m sure like most of us you dress, speak and behave at work in a certain way , because you have to. And you do lots of things at home (housework maybe or tax returns or sticking to the speed limit or paying your council tax bill ) because you have to.
For some of us, we have got to used to doing certain things , we Didn’t even realise what a chore it was and how much we hated it, until lockdown changed things. These boards are full of women saying how free they feel not having to perform femininity all day every day (although I accept there are other who say they miss it ). Some say they are scared to stop doing it as they will ‘ let themselves go’.
These don’t sound like free choices to me.
I’d love to run away and backpacking round SE Asia for 6 months but I can’t because I have a job / mortgage / kids / whatever.
Everyone makes compromises . No one is 100% “ themselves “ all the time . We all conform to social roles and expectations.
Your son is not the only teenager in his school who struggles with identity, who he is, what to wear, who to be friends with. They all do, it’s just that some hide it better.
He hides his taste in clothes, others hide their sexuality, religion , ethnicity and other things that are a key part of their identity. If he looks around him carefully and listens to others stories he will learn who they are.
That might help him build bridges.