The Celluloid Closet (1995)
Chosen by me from a list of free movies online.
A mostly fascinating look at the portrayal of homosexuality in cinema over the years. But more interesting is the way 'straight' films could be read as gay by an audience (often but not always intended by the film makers) desperate for sympathetic identification and whether bad representation is better than no representation.
Carefully selected clips can take on a different skew placed in this context (I am a great believer in art leaving the creator and forming a second life in the mind of the consumer - ask me sometime what I think Predator is really all about).
It takes a narrow focus on a simple straight/homosexual mode (a more modern update would maybe start to consider more transgender and asexual readings as sex is far more complicated than even this film would have).
It keeps things breezy and hopeful and is all the better for it but it does seem a little naive at the end.