We begin with a narrator discussing a missing painting by the fictional painter Tonnere. We then join collector Jean Rougel, who has six other paintings by the artist. Using them, a series of people in various tableaux vivantes, minor details in each painting, and a fictional roman a clef novel, he concludes what the absent painting looked like, what the series means, and then to reject his own hypothesis, because he finds it distasteful.
Raúl Ruiz' black-and-white mockumentary can be viewed as a burlesque of the art documentary that infests high-minded television shows. It certainly goes around Robin Hood's barn to do so. It can also be viewed as the sort of detail-obsessed reasoning that infuses novels like The Da Vinci Code, the Q-Anon conspiracy, and the tendency of many modern neo-fascists to see a series of vast conspiracies motivating everything they disapprove of, with the lack of evidence engorging the reach of such conspiracies, and their failures to predict what happens next as evidence of false-flag operations, or some longer-range effort, with an exhortation to "stick to the plan."
Having been brought up in an atmosphere of evidence-based rationality, I find such hypotheses to be idiotic. I believe that you notice events, work up a hypothesis, use the hypothesis to make predictions, and use the success or failure of those predictions to verify or falsify the hypothesis. Those who believe in these elaborate theories, when confronted with falsifying events, merely make their hypotheses more elaborate, adding epicycles to the epicycles to the epicycles of their assumptions. Neither are my personal wishes and tastes matters to be considered -- although as a fallible man, I am subject to the same flaws as Rougel.
All of which is a long-winded way of saying that this movie is a long exercise in seeing evidence in details that, like as not, are of no importance. The fictional Tonnere's details may be significant, but they may also be simply habits, or callbacks to other works, what are called "Easter Eggs" by the the detailed-obsessed, pseudo-rational loonies that infest our society. I have better ways to spend my time than to seek out meaning in nonsense, and find works like this, making obscure digs at the despicable, a bore.