There’s absolutely nothing wrong with headcanons but the problem starts when it’s supposed to be the only interpretation and the right one. Also, it’s not a good look when you insist every feminine guy is a trans girl. Do you know what it looks like when you call every woman who is even slightly masculine a trans man? It gives off the sense that you think women can’t be strong and those who are aren’t actually women. The same applies here. It makes it seems like you think men can’t be feminine and the only ones who can be feminine are actually women. This also reinforces archaic gender roles which I thought we’ve long moved past.
If you want to headcanon every feminine guy as trans woman, more power to you but please stop calling people transphobes for not interpreting the character the same way when it’s not canon that they’re trans.
