Here's something to try if none of the previous suggestions work (although use at your own risk!)... Locate your ....pbxproj file and make a copy, just in case anything messes up. Open the ....pbxproj for editing, search for productRefGroup and delete that line. Save the edit and re-open Xcode. Products directory shows back up! Summary: I'm not sure if productRefGroup is really necessary! Everything seems to build fine without it.

Check out: https://github.com/ethanhuang13/CupertinoJWT It works great, might be helpful for you!

I get this same error on latest Mac Catalyst, and similarly, the same code works perfectly on iOS in my case as well. This is specific to MPMusicPlayerController.applicationQueuePlayer (if I use .systemMusicPlayer instead, it does work on Catalyst... but systemMusicPlayer is not the behavior I want). Anyone else experience this? Should we submit it as a bug to Apple?

You'll have to use those names to call the web service to do a catalog search for the identifier, via https GET to api.music.apple.com and e.g. /v1/catalog/\(countryCode)/search. There's an example of this in Apple's sample code called "Interacting with Apple Music Content"/Adding-Content-to-Apple-Music - https://developer.apple.com/sample-code/wwdc/2017/Interacting-with-Apple-Music-Content.zip and explained in the video at WWDC 2017 Introducing MusicKit - https://developer.apple.com/videos/play/wwdc2017/502/.