I didn’t know ‘sex isn’t real’ was one of Judith Butler’s ideas. I just looked her up on the wiki link but could not make head nor tail of her rationale for this view. Gender yes but sex? Still not getting it. This is from the wiki piece:
The performance of gender is not voluntary, in Butler's opinion, and she believes the gendered, sexed, desiring subject must be constructed within what she calls, borrowing from Foucault's Discipline and Punish, "regulative discourses." These, also called "frameworks of intelligibility" or "disciplinary regimes," determine in advance what possibilities of sex, gender, and sexuality are socially permitted to appear as coherent or "natural."[citation needed] Regulative discourse includes disciplinary techniques that coerce the stylized actions and thereby maintain the appearance of "core" gender, sex and sexuality
I think I would be in the bottom set for Gender Studies.