@PB1961 your son has many interests. Your original post mentions art, music, musical theater, history, English, film, philosophy and an interest in politics. )And not math/science.) There is nothing wrong with going into college undecided. And regardless of major, or no major yet, he can submit supplement(s).
I know music majors, both BM and BA, who have gone on to doctorates and teaching at the college level. I know one who became a scholar in Medieval Studies, one who works for Sesame Street in a non-music area, one who started a collective of dancers, musicians and composers, one who went to law school, and a few who play in ensembles/freelance. That’s just music…I could continue regarding the other interests.
My main point is there is no need to know major or career when entering college, and there is time to explore. And career or grad/professional school do not have to relate to undergrad major.
It seems to me that the main decision may be whether to pursue certain interests like music, art or musical theater as a course of study or as extracurriculars. He doesn’t necessarily have to figure that out now but it may help guide his application choices.