The musical note icon is how you show individual tracks instead of sub-playlists.

Works like this:

- If you have a playlist that is all just individual tracks, then they will all show by default.

- If you have a playlist that is all just sub-playlists, they they will all show by default.

- If you have a playlist that is a combination of sub-playlists and individual tracks, then it will only show the sub-playlists, and hide the individual tracks behind that musical note icon.