What is left wing? People who seek social change, often by the state, to improve equality and address inequity and structural oppression?
Is sex one of the things about a person that affects their lives and access to fulfilment? I'd say yes. Is it someone's intrinsic sex that affects that, or the perception of their sex by others? I'd say most of the time their intrinsic sex. Eg violent attacks on transwomen are quite often homophobic - ie on men perceived as not doing masculinity right, rather than on perceived women.
How is the left wing helped by removing discussion of intrinsic sex? It isn't. And some of the consequences of trying to remove the vocabulary of sex from discussion make the left wing yet again look like they are much more concerned with midddle class people saying the right words than actual liberation of women, whether those women have transitioned or not.