Preventing UWP Suspension

app.xaml.cs

sealed partial class App : Application
{
    public App()
    {
        InitializeComponent();
        Suspending += (s, e) => Helpers.ShowToast("Suspending");
        Resuming += (s, e) => Helpers.ShowToast("Resuming");
        Helpers.SetupExSession(
            allowed: () => Helpers.ShowToast("Allowed"),
            denied: () => Helpers.ShowToast("Denied"),
            revoked: () => Helpers.ShowToast("Revoked"));
    }

    protected override void OnLaunched(LaunchActivatedEventArgs e)
    {
        if (!(Window.Current.Content is Frame frame))
        {
            Window.Current.Content = frame = new Frame();
        }
        if (e.PrelaunchActivated == false)
        {
            if (frame.Content == null)
            {
                frame.Navigate(typeof(MainPage), e.Arguments);
            }
            Helpers.ShowToast("Launched");
            Window.Current.Activate();
        }
    }
}

public static class Helpers
{
    public static void ShowToast(string text)
    {
        var content = new ToastContent
        {
            Visual = new ToastVisual
            {
                BindingGeneric = new ToastBindingGeneric
                {
                    Children =
                    {
                        new AdaptiveText { Text = text }
                    }
                }
            }
        };
        var toast = new ToastNotification(content.GetXml());
        ToastNotificationManager.CreateToastNotifier().Show(toast);
    }

    public static async void SetupExSession(Action allowed, Action denied, Action revoked)
    {
        var session = new ExtendedExecutionSession
        {
            Reason = ExtendedExecutionReason.Unspecified
        };
        session.Revoked += (s, e) => revoked?.Invoke();
        var result = await session.RequestExtensionAsync();
        switch (result)
        {
            case ExtendedExecutionResult.Allowed:
                allowed?.Invoke();
                break;
            default:
            case ExtendedExecutionResult.Denied:
                denied?.Invoke();
                break;
        }
    }
}

You should be able to replace the app.xaml.cs of any new blank UWP project and test this.