Show BusyIndicator while page is loading in MVVM

protected void ShowBusy(bool show)
{
    DataTemplate contentTemplateView = new DataTemplate(() =>
    {
        StackLayout stack = new StackLayout();
        _busyIndicator = new SfBusyIndicator();
        _busyIndicator.ViewBoxHeight = 100;
        _busyIndicator.ViewBoxWidth = 100;
        _busyIndicator.IsBusy = true;
        stack.Children.Add(_busyIndicator);
        return stack;
    });
 
    _popupLayout.PopupView.HeaderTitle = string.Empty;
    _popupLayout.PopupView.ContentTemplate = contentTemplateView;
    _popupLayout.PopupView.ShowHeader = false;
    _popupLayout.PopupView.PopupStyle.BorderColor = Color.Transparent;
    _popupLayout.PopupView.ShowFooter = false;
    _popupLayout.PopupView.ShowCloseButton = false;
    _popupLayout.PopupView.AutoSizeMode = AutoSizeMode.Height;
    _popupLayout.PopupView.BackgroundColor = Color.Transparent;
 
    _popupLayout.IsOpen = show;
 
}

//If you start here, and then click the Button to Page B this works
await NavigationService.NavigateAsync("NavigationPage/MainPage");
 
 
//If you start here, you will see a failure
//await NavigationService.NavigateAsync("NavigationPage/PageB");

<controls:BusyIndicator xIsBusy="True" />

public BusyIndicator()
{
    InitializeComponent();
 
    ctrlPopupLayout.SetBinding(SfPopupLayout.IsOpenProperty, new Binding("xIsBusy", source: this));
 
    // I cant access ctrlBusyIndicator here:
    ctrlBusyIndicator.SetBinding(SfBusyIndicator.IsBusyProperty, new Binding("xIsBusy", source: this));
}

private async void ShowDialog()
{
    ShowBusy = true;
 
    await Task.Delay(2000);
 
    ShowBusy = false;
    
    _dialogService.ShowDialog("BusyDialog", new DialogParameters() { { "message", "from main view model" } });
}