Not unrelated to Platform in mood is Five easy pieces (Bob Rafaelson, 1970).
Much as I love the iconic diner scene, there’s far more to it than that. Among its many virtues, it is a moving exposé of the pressures and frustrations of the classical musician’s life.
In those heady times (The king of Marvin gardens, The last detail… those were the days) before Jack Nicholson began impersonating himself, his final monologue before his mute father is overwhelming (sorry, better if you can watch the whole film, of course!):