Moving ID from AU to USA - What happens to my playlists?

Depends on where the music in those playlists comes from.

If these are playlists that are formed by tracks from the Apple Music subscription service, then yes, they may be empty, since you need to cancel the subscription and let it expire before you can change your Apple Account's region.

If the playlist are made from music ripped from CDs or purchases, then they should not be affected or only lose purchased tracks that are not available in the new region and have not been downloaded onto your device.

Downloaded tracks and tracks ripped from CDs or obtained from other sources should remain intact after the region change.

Welcome.

solomani wrote:

Thank you. So will look to potentially export the list at least and re-add after I migrate (yes it’s mostly Apple Music).

I guess I will also need to make sure iCloud files are locally stored as well.

Yes, if you are subscribed to iCloud+, you would need cancel that, and anything exceeding 5GB would likely be deleted.

Or I could create a new ID but that means switching as needed.

That option may present issues, as you can only switch Apple accounts once every 90 days.

click here ➜ View and remove your devices that are associated with your Apple Account for purchases - Apple Support