Examples:
Rimuru Tempest - Actually pretty simple case, character has mind of cis guy and identifies as a boy, while having sexless, but femine appearance.

Opera-san - unknown, several cases of being called a girl and not minding it, wearing femine clothes in youth but knowing that crossdressing is a reoccurring comedy theme opera still can be either or neither if it even would be revealed. My favorite joke is - their canon gender is "Yes"

Oh crap, it is actually fun talking about it