I have this problem too - did you ever come up with a proper solution to this? Switching out the declaration in the App class gets Core Data previews working again but swapping this out every time I want to build or preview is even more annoying than just not using previews. Also interesting to note this only happens when macOS is the preview target - setting the preview target to an iOS/iPadOS device continues to work without issue.

I think I have managed to resolve this myself - I created a new object wrapper to resolve a different issue and it has ended up resolving this issue too. import SwiftUI import CoreData struct ObjectsCommandMenu: Commands {   var context: NSManagedObjectContext   @CommandsBuilder var body: some Commands {     CommandMenu("Objects") {       NavigationLink(         destination: { NewObjectWrapper(context: context) },         label: { Text("New Object") }       )         .keyboardShortcut("o", modifiers: [.command, .shift])       Divider()       // more commands here     }   } } struct NewObjectWrapper: View {   var context: NSManagedObjectContext   @StateObject var object: Object   @ViewBuilder var body: some View {     ObjectEditor(object: object)   }   init(context: NSManagedObjectContext) {     self.context = context     self._object = StateObject(wrappedValue: Object(context: context))   } }

For anyone still having this issue - I used the following code blcok in my App.swift definition to have it work without swapping it around each time: #if DEBUG let dataStore = { if (ProcessInfo.processInfo.environment["XCODE_RUNNING_FOR_PREVIEWS"] == "1") { return DataStore.preview } else { return DataStore.shared } }() #else let dataStore = DataStore.shared #endif This little code block seems to let me work across all devices without having to swap anything around. I still can't see why this happens - it definitely isn't needed for the default template so I'm guessing there's some recursion going on somewhere in the app where the datastore is getting instantiated a second time; perhaps to do with how I'm setting up either my Commands menu or my Preferences window (as both of these take the viewContext as either a parameter or an environment respectively).