AppDelegate.swift

import UIKit
import BackgroundTasks

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    // app data, just contains a lastUpdateTime property that is set whenever
    // handleAppRefresh is called as a way to validate the bgFetch is being triggered
    // by iOS
    //
    let timeViewModel = TimeViewModel()

    let appRefreshIdentifier = "com.esri.dev.timekeeper.refresh"

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        BGTaskScheduler.shared.register(forTaskWithIdentifier: appRefreshIdentifier, using: nil) { (task) in

            self.handleAppRefresh(task: task as! BGAppRefreshTask)
        }

        return true
    }

    func scheduleAppRefresh() {

        print("Scheduling app refresh...")

        let request = BGAppRefreshTaskRequest(identifier: appRefreshIdentifier)
        request.earliestBeginDate = Date()

        do {
            try BGTaskScheduler.shared.submit(request)
        } catch {
            print("Failed to submit task: \(error)")
        }
    }

    private func handleAppRefresh(task: BGAppRefreshTask) {

        print("handling app refresh....")

        scheduleAppRefresh()

        // - make network request to fetch data
        // - serialize data, if necessary
        // - dispatch to main to update
        //
        DispatchQueue.main.async {
            self.timeViewModel.lastUpdatedTime = Date()
            task.setTaskCompleted(success: true)
        }
    }

    // MARK: UISceneSession Lifecycle

    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }
}

SceneDelegate.swift

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

        guard let timeViewModel = (UIApplication.shared.delegate as? AppDelegate)?.timeViewModel else {
            return
        }

        // Create the SwiftUI view that provides the window contents.
        let contentView = ContentView().environmentObject(timeViewModel)

        // Use a UIHostingController as window root view controller.
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: contentView)
            self.window = window
            window.makeKeyAndVisible()
        }
    }

    func sceneDidEnterBackground(_ scene: UIScene) {

        guard let appDelegate = (UIApplication.shared.delegate as? AppDelegate) else {
            return
        }

        appDelegate.scheduleAppRefresh()
    }
}