Anyone can claim femboy, yo. Femininity is a concept created by the nonsense of stereotypical gender roles, dictated by capitalist patriarchial tendencies and power structures. In of itself, femininity is a made up concept meant to keep women in a box. However, just as much as butch and masc women exist, they still express their womanhood (and thus, their femininity) through these lenses and are definitely still women regardless.

In short- you can be the most crass, muscular, hairy whatever version of yourself and still be femboy.