Only the original thread that created a view hierarchy can touch its views - what is the cause?

Hello. The question has been asked in the forum previously but the source of the problem is different for each developer and the limited answers don't help my case.

I use a pattern to display a splash screen in my app that works for a previous app. It goes as follows:
1. In App.Xaml.cs I call MainPage = new NavigationPage(new SplashPage());
2. In SpashPage's OnAppearing method I call App.Current.MainPage = new NavigationPage(new FPMainPage());

Below is the code:

      public App()
        {
            Syncfusion.Licensing.SyncfusionLicenseProvider.RegisterLicense("***");

            InitializeComponent();
            MainPage = new NavigationPage(new SplashPage());
        }
...
namespace FP.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class SplashPage : ContentPage
    {
        public SplashPage()
        {
            InitializeComponent();
            NavigationPage.SetHasNavigationBar(this, false);
        }

        protected override async void OnAppearing()
        {
            base.OnAppearing();

            await splashImage.ScaleTo(0.9, 500, Easing.Linear).ConfigureAwait(false);
            await splashImage.ScaleTo(0.6, 200, Easing.Linear).ConfigureAwait(false);
            await splashImage.ScaleTo(0.3, 200, Easing.Linear).ConfigureAwait(false);
            await splashImage.ScaleTo(0.0, 200, Easing.Linear).ConfigureAwait(true);

            App.Current.MainPage = new NavigationPage(new FPMainPage());
        }
    }
}
...
public FPMainPage()
        {
            BindingContext = _viewModel;

            InitializeComponent();
        }

        protected override void OnAppearing()
        {
            try
            {
                base.OnAppearing();
                _viewModel.LoadData();

                _nextSchedule = _viewModel.EarliestSchedule();

                foreach (ItemGroup<string, Game> item in ListViewGames.ItemsSource)
                    if (_nextSchedule == item)
                    {
                        ListViewGames.SelectedItem = item;
                        ListViewGames.ScrollTo(item?.FirstOrDefault(), Xamarin.Forms.ScrollToPosition.Start, true);
                        break;
                    }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.Message);
            }

        }

The error occurs at FPMainPage InitializeComponent. What change do I need to make so that it works?

Thank you!