Update: I realized two changes to fix the problems: I have to import Combine and CoreData in my DataController.swift (before only CoreData) I have to import SwiftUI and CoreData in my xyzAPP.swift (containing @main) (before only SwiftUI). => Looks like we have to import a lot more nowadays

'Error' occurred after updgrading from 16.4 to 26 Importing combine solves the problem of an empty class XYZ: ObservableObject When using CoreData in a Swift App, I was used to have a Class 'DataController : ObservableObject' to manage the CoreData Stack. In the past I was used to only import CoreData and everything works fine: // // Observable Object to enable Access to CoreData within the App // therefore include in @main: // ... 1. @StateObject var dataController = DataController() // ... 2. ContentView() // .environment(\.managedObjectContext, dataController.container.viewContext) // .environmentObject(dataController) import CoreData class DataController: ObservableObject { let container: NSPersistentCloudKitContainer init() { container = NSPersistentCloudKitContainer(name: "Main") container.loadPersistentStores { storeDescription, error in if let error { fatalError("Fatal error loading store: \(error.localizedDescription)") } } } // DO some stuff here func save() { if container.viewContext.hasChanges { try? container.viewContext.save() } } ... } Now I have to import Combine and add Protocol stubs to get rid of the error. Something must have change "under the hood of Xcode"?