I just created a new XF Projects targetting iOS, Android, UWP and WPF in Windows and decided to add macOS to it as well.
So I copied the project to a computer running macOS High Sierra and followed the instructions to add macOS to my existing shared project.
While I can still compile and run every other project in the shared project solution (obviously apart from UWP and WPF) on macOS, the macOS one does not build and generates the following error:
/Users/apple/Projects/vanxshop/VanX/VanX/VanX.macOS/VanX.macOS.csproj(11,11): Error MSB4226: The imported project "/Library/Frameworks/Mono.framework/Versions/5.10.1/lib/mono/xbuild/Xamarin/Mac/Xamarin.Mac.CSharp.targets" was not found. Also, tried to find "Xamarin/Mac/Xamarin.Mac.CSharp.targets" in the fallback search path(s) for $(MSBuildExtensionsPath) - "/Library/Frameworks/Mono.framework/External/xbuild/" and "/Applications/Visual Studio.app/Contents/Resources/lib/monodevelop/AddIns/docker/MonoDevelop.Docker/MSbuild" . These search paths are defined in "/Users/apple/Library/Caches/VisualStudio/7.0/MSBuild/45652_1/MonoDevelop.Projects.Formats.MSBuild.exe.config". Confirm that the path in the declaration is correct, and that the file exists on disk in one of the search paths. (MSB4226) (VanX.macOS)