If “The Man Who Killed Hitler and Then the Bigfoot” (2019) isn’t a fable about post-traumatic stress disorder, it ought to be. And if it is, it’s the best one I’ve ever seen. Sam Elliott (who is having quite the late-life renaissance), is The Man. One of the greatest of The Greatest Generation, we find him in 1987. Outwardly, a quiet retirement. Inside, the silent torment of his memories of love and war, which we see in flashback. He needs something to get him out of this purgatory. Fortunately, there’s a monster to slay, literally, but I also think figuratively.