I think it’s just one of the theme songs. Often shows release a full OST including the background music instrumentals, but usually at the end of a show or after it’s finished airing. So I’d suggest keeping an eye out for that.
Do you know the jazzy song with female voice they keep playing in come back ahjussi? I think it’s also played at the end of ep 12. I search the ost but I can’t find it
The Obsessive Dilettante 