OnDiscoveryClicked.cs

private void OnDiscoveryClicked(object sender, System.EventArgs e)
{
    if (App.Current.MainPage is TabbedPage mainPage && sender is Button button)
    {
        mainPage.CurrentPage = mainPage.Children[0];
        Tab1.TextColor = Color.Gray;
        Tab2.TextColor = Tab3.TextColor = Color.DarkGray;
    }
}