Far from War (1987)

An elderly veteran of WWII living in peaceful retirement with his son and the latter's family becomes increasingly lost in wartime memories and reminiscences, much to his son's consternation. One day, an item the old man reads in a magazine prompts him to go off unannounced on a war-related quest. The son goes searching for his father, and in doing so reaches a greater understanding of both the old man and the generation he represents.

Unfortunately the movie Far from War is not yet available on HBO Max.