Deploy checkboxes disabled in Configuration Manager
Since Xamarin 3.5, Xamarin.iOS projects deployed automatically whenever you press the Start toolbar button or pick the Debug > Start Debugging menu item. You will still need to set the desired Xamarin.iOS app project as the StartUp Project before before running either of those commands.
Because of this, the Deploy checkboxes are intentionally disabled in the Visual Studio Configuration Manager for Xamarin.iOS projects:
This change eliminates an error that could appear in older versions of Xamarin (version 3.3 and earlier) when the Xamarin.iOS app project was not set to deploy: