Mon oncle d’Amérique contains three elements: a neurological/psychological lecture, a melodrama of three intersecting lives, and scenes from black and white French movies. Presumably, these elements are supposed to add up to an artistic unity, but they work against each other instead, so that the net result is irritating. Especially confusing is the way the backgrounds of the three major characters are presented as if someone is hurriedly reading their dossiers.
If the entire film were simply a discussion on neurology and psychology, it might have been interesting. If it were just a melodrama, it might have been enjoyable. But the combination of the two creates the feeling that we are being talked down to. Over and over we are told that our conscious mind thinks it has reasons for what it does, but we are duped by our unconscious. No doubt, that is sometimes the case. But intercut with the melodrama, this lecture condescendingly suggests that we would not be able to understand these people and what they do without the benefit of the lecture.
References to American uncles are reminders that we live lives of illusion, since people express doubts about these uncles. The gratuitous scenes from old movies presumably are supposed to reinforce this notion of the illusory conscious mind.
The movie as a whole is less than the sum of its parts.