Original title (FR): Reflet dans un diamant mort (Reflection in a Dead Diamond)

When the mysterious woman in the room next door disappears, a debonair 70-year-old ex-spy living in a luxury hotel on the Côte d'Azur is confronted by the demons and darlings of a lurid past in which moviemaking, memories and madness collide.

https://www.themoviedb.org/movie/1013446-reflet-dans-un-diamant-mort