kids who are known 'gender transgressors' and have been using school as a safe place to express themselves”
Schools aren't places to express your identity, they are places to learn in safety.
Kids should 'transgress' social norms at weekends.
That's why I don't think boys need to be allowed to wear dresses, wearing a dress is not essential for anyone, if you can't wear one at school and have to wear trousers like the other boys, you'll be ok.
Fashion choices are not an essential part of your being. Temporary arbitrary dress codes don't harm you even if you don't like them.
You'd have to prove boys not wearing dresses is somehow harmful. With girls and trousers a utility argument was made and won.
If you just argue kids should be able to wear what they want to express themselves then you'd surely argue for no restrictive dress codes at all? No uniform.
Then if a child wanted to come to school dressed as a cat, why should they be stopped? If it's their identity expression?
After all, nearly everything we wear are just arbitrary current cultural dress codes.
A boy doesn't need to wear a dress.
Any more than I need to wear a top hat.
They're just fashion choices. School isn't about expressing your fashion preferences.