for myself - .NET Standard links - to review it later

https://channel9.msdn.com/Shows/XamarinShow/Snack-Pack-15-Upgrading-to-XamarinForms-to-NET-Standard

https://blog.xamarin.com/building-xamarin-forms-apps-net-standard/

https://forums.xamarin.com/discussion/95916/works-xamarin-forms-net-standard-entity-framework-core-for-sqlite-on-ios-android-uwp

https://stackoverflow.com/questions/44287464/any-way-to-use-net-library-in-pcl-project

https://forums.xamarin.com/discussion/76039/sharing-assemblies

https://stackoverflow.com/questions/39050911/net-standard-net-core-pcl

https://github.com/dotnet/project-system/issues/783

https://docs.microsoft.com/en-us/dotnet/standard/net-standard

https://blog.xamarin.com/share-code-net-standard-2-0/

https://forums.xamarin.com/discussion/75989/xamarin-forms-nuget-package-on-a-net-standard-portable-project

https://oren.codes/2017/04/23/using-xamarin-forms-with-net-standard-vs-2017-edition/

https://xamarinhelp.com/dot-net-standard-pcl-xamarin-forms/

https://github.com/adamped/XamarinForms.NetStandard/blob/master/XamarinForms.NetStandard/XamarinForms.NetStandard/XamarinForms.NetStandard.csproj

https://forums.xamarin.com/discussion/86139/targeting-net-standard

https://github.com/fsprojects/Paket/issues/1883

https://forums.xamarin.com/discussion/99084/acr-user-dialogs-not-working-in-android-pcl

https://github.com/aritchie/userdialogs

https://stackoverflow.com/questions/38127534/acr-userdialogs-pcl-error

https://forums.xamarin.com/discussion/67466/unable-to-build-the-xamarin-with-linker-option-sdk-assemblies

https://forums.xamarin.com/discussion/96494/could-not-load-assembly-xamarin-android-support-fragment