using Xamarin.Forms.PlatformConfiguration.iOSSpecific;

 ...

On<Xamarin.Forms.PlatformConfiguration.iOS>().SetUseSafeArea(true);

xmlns:ios="clr-namespace:Xamarin.Forms.PlatformConfiguration.iOSSpecific;assembly=Xamarin.Forms.Core"
ios:Page.UseSafeArea="true"

Error CS1061: 'IPlatformElementConfiguration<iOS, Page>' does not contain a definition for 'SetUseSafeArea'

On<Xamarin.Forms.PlatformConfiguration.iOS>();