No one would know he’s transgender. He would have no problem using the men’s room.
I want to emphasize that from a moral standpoint, I oppose sex change surgery. However, in the real world I live in, answers to these questions aren't that easy.
So, this "guy" either breaks the law and uses the men's room. Or he obeys the law and causes outrage.
Or, perhaps we don't let this individual pee in public. Or maybe we kidnap "him" and cut off his junk and give him implants and make him be a woman?
There just aren't easy answers to this, and people pretending they have the one-size-fits-all absolute moral, conservative answer on this aren't helping.