How to enable addToCloudMusicLibrary?

Our app accesses Apple Music and the user's music library. It is installed & running fine on lots of iOS devices.

Thanks to a recent release using Catalyst it's also now installed & running fine on a number of Mac's.

However we've just had an error reported by one of our Mac users which I don't understand. Specifically:

• The app is connecting to the user's Apple Music account no problem

• It then asks for cloud capabilities

• instead of getting both musicCatalogPlayback and addToCloudMusicLibrary (as we'd normally expect) it's only getting the former. Our app requires addToCloudMusicLibrary to operate.

So in the code snippet below it prints "No add to library capability":

Code Block 
SKCloudServiceController().requestCapabilities { (cloudServiceCapability, error) in
    if let error = error {
        print("Error: \(error.localizedDescription)")
        return
    }
    guard cloudServiceCapability.contains(.musicCatalogPlayback) else {
        print("No music catalog playback")
        return
    }
    guard cloudServiceCapability.contains(.addToCloudMusicLibrary) else {
        print("No add to library capability")
        return
    }
    print("Good to go")
}

My initial assumption was that the user had not enabled iCloud Sync, but this has clearly been enabled.

What else could cause this?

The Mac in question is an M1 MBP. We don't have many M1 installs so I'm somewhat concerned this could be an M1 / Catalyst issue.

Thanks in advance.