Cold Head (1970)

Shots of a car speeding down the road are intercut with kinky sex flashes (a woman with a whip rides a guy, for instance). Then the car crashes into a tree, the male driver (Christian Chaix) is decapitated and the bloody, injured female (Marie-Paule Mailleux) scoops up his head and returns to her home. There, she cleans herself and the head off, prepares dinner for herself and the head, buys the head a Ken Doll to keep it company, puts the head on a mannequin's body and then has a series of strange hallucinations, which include having sex with her bloodied lover, dancing in a room by herself with a spotlight, etc. Things culminate in her having sex with the head and then throwing it into the trash bin.

Unfortunately the movie Cold Head is not yet available on HBO Max.