Why is my iMac stuck on "Loading Cloud Music Library"?

If you're not paying for Apple Music or iTunes Match then the Sync Library setting should be turned off on each computer and device. Ideally you turn those off before your subscription elapses so there is some potential to recover from any unexpected surprises, e.g. lack of access to all (non-iTunes Store) music currently located only in the cloud and not on your computer or device.

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Music > Settings > General > turn off Sync Library.

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I have the same issue and did go ahead and try turning off Sync Library. Unchecked the box, hit Okay, closed the window. "Loading Cloud Music Library..." was still showing up (both bottom left and at the top of my screen), so I opened Settings again, and the box had re-checked itself! Any further ideas? I left my laptop on all night to see if it just needed more time to upload everything, but every song in my library already has the "The song, album, or playlist is downloaded to your computer" symbol next to it.

When I go to check Music on my phone (logged in under the same Apple ID on iOS, Sync Library turned on), some songs have downloaded, but a large percentage say "This item is not synced across your devices," and then urge me to go turn on Sync Library on my Mac.

Hmm. That's odd. Try closing Music, then hold down option+cmd when you launch it again.

Failing that try holding down just option when you relaunch and see if you can create a new library, e.g. Music 2, see if that opens without an interminable iCloud Music Library download. Then see if you can switch back to the original library and see what happens.

You might also look inside your Music Library.musiclibrary package (right-click > Show package contents) to see what is inside. Multiple .tmp files would indicate something is going wrong as the library tries to update its various component files.

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Tick the three options under/beside Show:

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