How to recover Apple Music library after switching carriers on iPhone 16 Pro Max?

I upgraded to a new phone, IPhone 16 Promax. I haven’t really been able to figure out what to do to get this resolved on my own, so I came here.

[Re-Titled by Moderator]

Original Title: i had apple music through one carrier and always had my sync on. When i switched to a different carrier my music disappeared. What happened and what do i do to get it back? i still have the same Apple ID and everything is the same.