Femme is a kind of gender expression where an individual presents and acts in a feminine manner. Femme is a type of gender expression and is different from a gender identity.
Sources:
https://theswaddle.com/the-various-gender-identities-and-gender-expressions-explained/
https://affirmativecouch.com/are-you-femme-what-femme-isnt-and-what-it-is/
https://www.verywellmind.com/what-is-femme-invisibility-5187233