Is it possible it’s counted as a subcategory of gilui arayos? IIRC the Gemara considers a Ben Noach to be metzuveh on not being mesares themselves or even animals because of gilui arayos. The Rambam lists it in Issurei Biah as well.
Seems to be a מחלוקת ראשונים how to pasken in regards to סירוס for בני נח see בית שמואל סימן ה ס״ק ט”ז.
Also, I think a distinction can be drawn between סירוס, which is a one time action that is over and done with, and לא תלבש, which is an ongoing issur and you’re sort of approving of their active violation as Rabbi Raskin sees it by using their preferred pronoun.