I have been trying to get this to work as well, with no luck yet. Adding to the things you have tried, I have noticed the Widget is able to access CloudKit data for me, on my device, but fails to work for any one else on TestFlight. Hoping this is temporary during the beta. Any help would be extremely helpful. Thanks!

Can we access NSPersistentCloudKitContainer in the same way we do from the app, or will we need still need App Groups? I don't think CloudKit containers work with App Groups.