Lost Music Library and Playlists After Switching to Apple One

Upgrading to Apple One shouldn't impact your library. I started using iTunes Match, updated to Apple Music, and now also use Apple One. My iCloud Music library remained the same each time, though with Apple Music I've obviously been able to add more content to it which would be lost if I closed the subscription.

These are library syncing services, not backups. Ideally you would have all of your music stored on at least one computer and backed up for security. Do the MacBook Pro and iPhone 15 Pro still show the expected cloud content, playlists, etc. If so this is likely an issue with the library on the MBA. Reboot the computer, then try holding down option+cmd as you launch Music to open it in its safe mode. Make sure that you are signed into your Apple ID and that your computer is authorized to it. See Use Sync Library with your Apple Music subscription - Apple Support and try to turn on Sync Library once more.

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