You can’t use this version of the application <APP NAME> with this version of macOS.

That's not due to the new version of MacOS. See this: https://stackoverflow.com/questions/63399629/swiftui-fetchrequest-error-a-fetch-request-must-have-an-entity

They suggest here:

• https://developer.apple.com/forums/thread/652001

and here

• https://www.appsloveworld.com/swift/100/82/swiftui-fetchrequest-error-a-fetch-request-must-have-an-entity?utm_content=cmp-true

to have the context declare in struct App.

Could you try it ?

I'm not really sure what context you're talking about. I'm using the boiler plate code that Xcode makes when you click the CoreData checkbox. I noticed that if I comment out this part it crashes because it expects core data to return something so I'm not sure what to return in this case because I don't want to populate it with mock items/entries (incidentally I changed item to entry)

        let viewContext = result.container.viewContext
        for _ in 0..<10 {
            let newEntry = Entry(context: viewContext)
            newEntry.title = "test"
        }

This is the struct app

import SwiftUI

@main
struct iJournalApp: App {
    let persistenceController = PersistenceController.shared

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(\.managedObjectContext, persistenceController.container.viewContext)
        }
    }
}

and this is the content view

import SwiftUI
import CoreData

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext

    @FetchRequest(
        sortDescriptors: [],
        animation: .default)
    
    private var entries: FetchedResults<Entry>

    var body: some View {
        NavigationView {
            List {
                if entries.count > 0 {
                    ForEach(entries) { entry in
                        Text(entry.title ?? "Test")
                    }
                }
            }
            .toolbar {

            }
            Text("Select an item")
        }
    }

}


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

and here is the PersistenceController

import CoreData

struct PersistenceController {
    static let shared = PersistenceController()

    static var preview: PersistenceController = {
        let result = PersistenceController(inMemory: true)
        let viewContext = result.container.viewContext
        for _ in 0..<10 {
            let newEntry = Entry(context: viewContext)
            newEntry.title = "test"
        }
        do {
            try viewContext.save()
        } catch {
            // Replace this implementation with code to handle the error appropriately.
            // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
        return result
    }()

    let container: NSPersistentContainer

    init(inMemory: Bool = false) {
        container = NSPersistentContainer(name: "iJournal")
        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        }
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

                /*
                 Typical reasons for an error here include:
                 * The parent directory does not exist, cannot be created, or disallows writing.
                 * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                 * The device is out of space.
                 * The store could not be migrated to the current model version.
                 Check the error message to determine what the actual problem was.
                 */
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        container.viewContext.automaticallyMergesChangesFromParent = true
    }
}

So it turns out that this is a known bug

https://stackoverflow.com/questions/72242577/fetching-data-in-preview-a-fetch-request-must-have-an-entity-uncaughtexception