Hello I am having the same error.
I am developing on VS 2017 Windows machine linked to a mac. my applications builds and runs well on Android (verified after multiple QA runs).
However we are getting this native linking error when building on IOS. Using the newest version of ESRI maps nuget package for .NET. Both ESRI.Forms and ESRI.IOS are installed through nuget and I have tried both versions available just in case. Any help would be appreciated.
Error Native linking error: framework not found ArcGIS-sim64 RT.iOS C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets 747
Error Native linking error: warning: directory not found for option '-F/Users/vlad/Library/Caches/Xamarin/mtbs/builds/RT.iOS/9bd34334c2bb0c14c8bdf794fb67e9fc/framework'
RT.iOS C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets 747