NSFetchedResultsController with UITableViewDiffableDataSource update value

I have a NSFetchedResultsController combined with a UITableViewDiffableDataSource.

There is a bool attribute "marked" in my entity which I want to change by clicking on the table view cell. To display the status, I change the background color of the cell. However, the reload is not working as expected. The background color of the cell won't change.

I first tried UITableViewDiffableDataSource<String, NSManagedObjectID>, but obviously that won't work for changes, because the NSManagedObjectID doesn't change. I then updated it to UITableViewDiffableDataSource<Int, Test>, but that also didn't work as expected.

Any ideas how to solve this? Or is it just not (yet) possible?

import UIKit
import CoreData

class MainViewController: UITableViewController {
    
    lazy var fetchedResultController: NSFetchedResultsController<Test> =  {
        let fetchRequest: NSFetchRequest<Test> = Test.fetchRequest()
        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "timestamp", ascending: true)]
        let fetchedResultController = NSFetchedResultsController<Test>(fetchRequest: fetchRequest, managedObjectContext: self.viewContext, sectionNameKeyPath: nil, cacheName: nil)
        fetchedResultController.delegate = self
        return fetchedResultController
    }()
    
    var persistentContainer: NSPersistentContainer { get { return (UIApplication.shared.delegate as! AppDelegate).persistentContainer } }
    var viewContext: NSManagedObjectContext { get { return self.persistentContainer.viewContext } }

    lazy var dataSource: UITableViewDiffableDataSource<Int, Test> = {
        return UITableViewDiffableDataSource<Int, Test>(tableView: self.tableView) { (tableView, indexPath, cdObject) -> UITableViewCell? in
        
            let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
            
            cell.textLabel?.text = "\(cdObject.name!) (\(cdObject.id))"
            cell.detailTextLabel?.text = DateFormatter.localizedString(from: cdObject.timestamp!, dateStyle: .short, timeStyle: .short)
            cell.backgroundColor = cdObject.clicked ? UIColor.systemOrange : UIColor.systemBackground
            
            return cell
        }
    }()
    
    
    @IBAction func barButtonPressed_insert(_ sender: UIBarButtonItem) {
        for i in 0 ..< 7 {
            let newCDEntry = Test(context: self.viewContext)
            newCDEntry.id = Int16(i)
            newCDEntry.name = "Name \(i)"
            newCDEntry.timestamp = Date()
        }
        
        self.viewContext.transactionAuthor = "regular insert"
        defer { self.viewContext.transactionAuthor  = nil }
        do {
            try self.viewContext.save()
        } catch {
            let nserror = error as NSError
            if let conflicts = nserror.userInfo["conflictList"] as? [NSConstraintConflict] {
                for conflict in conflicts {
                    for conflictObject in conflict.conflictingObjects {
                        self.viewContext.delete(conflictObject)
                    }
                }
            }
            do {
                try self.viewContext.save()
            } catch {
                print("##### error saving insert")
            }
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        do {
            try self.fetchedResultController.performFetch()
        } catch {
            print("could not fetch data")
        }
        self.applyFetchedDataToDataSource(animated: false)
    }
    
    private func applyFetchedDataToDataSource(animated: Bool) {
        var snapshot = NSDiffableDataSourceSnapshot<Int, Test>()
        snapshot.appendSections([0])
        snapshot.appendItems(self.fetchedResultController.fetchedObjects ?? [])
        self.dataSource.apply(snapshot, animatingDifferences: animated)
    }
    
    @objc private func managedObjectContextObjectDidSave(notification: Notification) {
        print("received save notification")
        self.viewContext.mergeChanges(fromContextDidSave: notification)
    }
    
    // MARK: - TableView
    
    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)
        
        let cdObject = self.fetchedResultController.object(at: indexPath)
        cdObject.clicked = !cdObject.clicked
        do {
            self.viewContext.transactionAuthor = "click toggled"
            defer { self.viewContext.transactionAuthor  = nil }
            try self.viewContext.save()
        } catch {
            print("could not save clicked toggle")
        }
    }
}

extension MainViewController: NSFetchedResultsControllerDelegate {
    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        self.applyFetchedDataToDataSource(animated: true)
    }
}