A very unique ending

Augustus,

Not sure what examples of film noir you are referring to. I suppose The Killers comes to mind, but that uses a very different narrative format, specifically use of flashbacks. TLADIA does not do that, in effect what The Killers did in killing the protagonist and then telling his story, bringing him back, in flashbacks.

I would also point out it is simplistic to view TLADIA as a film in which Chance is the protagonist, at least in the sense that he is for the whole film. When the film begins, and thinking back to seeing it the first time, it seems that Jim Hart is the protagonist. He is in the opening, the focus on how his work is leading him to retire, the scenes in the bar followed by the talk of fishing and why he wants to go alone to the desert to investigate Masters. And then he goes, we see him alone investigating Masters, and then suddenly he is not anymore. At that point, who then is the protagonist? Masters? Or Chance?

Then there is the way that Masters and Chance in some ways are alter egos, almost using the kind of doubling comparators approach that Existentialist filmmakers like Antonioni and Bergman used from time to time. So does that mean that there is no single protagonist, more like a dual antagonist/protagonist role played by both? The antihero nature of Chance's character is part of that imo non-standard mode of presentation while also making him more like Masters's alter ego than a conventional protagonist facing Masters as the antagonist.

Just to add to the complexity it is not even always a clear case of antagonism between them, as the way Masters considers the futility of his life and work makes him somewhat sympathetic to Chance's goal even though that is to arrest or perhaps even kill Masters.

Add in that secondary characters at times take on a significance that makes the whole approach seem more ensemble in nature than about a story focused on a primary character.

Part of that involves adding Vukovich as a comparator to Chance, and eventually to make that clear he literally becomes Chance's successor, becoming like Chance? As the film ends, who is the protagonist?

I can't think of a noir film that comes close to this kind of narrative complexity as regards the question who the film is about. Of course I think this works as it is all in service of the film's overall theme of counterfeiting as a metaphor for how people present misleading and inauthentic personas. But that is another matter.