How to preview Core Data data inside SwiftUI Previews

Here is a demo of what I have (kind of a lot of code, but I hope someone can follow it).
I have one entity inside Core Data named Activity with one string field. For that I use this extension to display the data in the Previews:

extension Activity {
    var _name: String {
        name ?? ""
    }
    
    static var example: Activity {
        let controller = DataController(inMemory: true)
        let viewContext = controller.container.viewContext

        let activity = Activity(context: viewContext)
        activity.name = "running"
        
        return activity
    }
}

For setting up Core Data I use a DataController object:

class DataController: ObservableObject {
    let container: NSPersistentCloudKitContainer
    
    init(inMemory: Bool = false) {
        container = NSPersistentCloudKitContainer(name: "Model")
        
        if inMemory {
            container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
        }
        
        container.loadPersistentStores { storeDescription, error in
            if let _ = error {
                fatalError("Fatal error loading store")
            }
        }
    }
    
    static var preview: DataController = {
        let dataController = DataController(inMemory: true)
        let viewContext = dataController.container.viewContext
        
        do {
            try dataController.createSampleData()
        } catch {
            fatalError("Fatal error creating preview")
        }
        
        return dataController
    }()
    
    func createSampleData() throws {
        let viewContext = container.viewContext
        
        for _ in 1...10 {
            let activity = Activity(context: viewContext)
            activity.name = "run"
        }
        
        try viewContext.save()
    }
}

In the app file I do the following setup:

struct TestApp: App {
    @StateObject var dataController: DataController
    @Environment(\.managedObjectContext) var managedObjectContext
    
    init() {
        let dataController = DataController()
        _dataController = StateObject(wrappedValue: dataController)
    }
    
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(\.managedObjectContext, dataController.container.viewContext)
        }
    }
}

In my ContentView I display a list of this string from Core Data, which works correctly:

struct ContentView: View {
    let activities: FetchRequest<Activity>
    
    init() {
        activities = FetchRequest<Activity>(entity: Activity.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \Activity.name, ascending: false)], predicate: nil)
    }
    
    var body: some View {
        List {
            ForEach(activities.wrappedValue) { activity in
                ActivityView(activity: activity)
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var dataController = DataController.preview
    
    static var previews: some View {
        ContentView()
            .environment(\.managedObjectContext, dataController.container.viewContext)
            .environmentObject(dataController)
    }
}

But in my ActivityView where I display the string in a simple text field, previewing doesn't work.

struct ActivityView: View {
    let activity: Activity
    
    init(activity: Activity) {
        self.activity = activity
    }
    
    var body: some View {
        Text(activity._name)
    }
}

struct ActivityView_Previews: PreviewProvider {
    static var previews: some View {
        ActivityView(activity: Activity.example)
    }
}

I can see the string "run" in my list, 10 times, the way it is setup, but in the ActivityView screen I don't see anything displayed in the preview.
Not sure why is that, I hope someone has an idea.

edit:

I also tried this in the preview, but still doesn't work.

struct ActivityView_Previews: PreviewProvider {
    static var dataController = DataController.preview
    
    static var previews: some View {
        ActivityView(activity: Activity(context: dataController.container.viewContext))
            .environment(\.managedObjectContext, dataController.container.viewContext)
    }
}