Half an hour well spent: I'm Thinking of Ending Things composer Jay Wadley on The Film Scorer podcast, where he talks about his approach to the film's score, the memory of music, and what it was like working with CK. One thing Wadley talks about at length: the music in the movie is largely meant to represent what Jake remembers (or misremembers) of tunes that he has heard--the ballet, for instance, is supposed to sound almost-but-not-quite the same as ballets you (or Jake) might have heard.
There's an audio version and Youtube version. Take yer pick!
Thanks to whitebearpr1 over on Reddit.