Hey, not a dev but from my experience playing this a lot in different ways I dont think it was the clothing choice. The puberty potion is meant to be a way to stop your character from undergoing female development and puberty.
Yep! However, your Mordred can still be non-binary/trans without the puberty potion, it just affects the sexual dimorphism your character will have (masculine or feminine features)
Edit: I have a trans/non-binary Mordred who's *very* late out of the closet (I'm thinking maybe adulthood if I get the chance?) and I'm pretty sure you still get gender things if you don't take the potions (shooting for a masc Mordred)