Why wouldn't it be? Just don't shove a bunch of weird unnecessary sexism stuff in there.
A good example of sexual dimorphism in a fantasy species is the imps from the Helluva Boss cartoon series. The biologically male imps have one horn pattern, and the biologically female imps have another. One of the characters has a sister who has the biologically male horns, indicating she is a trans woman. There's no comment on it, there's no stereotyping, no jokes made about it, etc., because she's just herself regardless of the roll of the genetic dice, even if it's on full display for all to see. Respectful representation does not prevent species from having different physical forms.