Hobbies / interests correlated with Big 5 scores? Are there any established treatments (I'm going to leave the exact terms a little bit vague because my understanding is vague) of which hobbies and interests are most likely to be attractive to someone with XYZ score on an  OCEAN / Big 5 test?

TIA,
Yes. One example is that people high in Openness to New Experiences are interested in aesthetic experiences including museums and being in nature, and novel experiences as you'd expect from the name. https://psycnet.apa.org/record/1997-08808-031

Treatment is a bit misleading here to mean 'study', because in psychology it usually means 'intervention'.