Assemblies removed from the ASP.NET Core shared framework
The most notable assemblies removed from the ASP.NET Core 3.0 shared framework are:
Newtonsoft.Json (Json.NET). To add Json.NET to ASP.NET Core 3.0, see Add Newtonsoft.Json-based JSON format support. ASP.NET Core 3.0 introduces System.Text.Json for reading and writing JSON. For more information, see New JSON serialization in this document.
Entity Framework Core
For a complete list of assemblies removed from the shared framework, see Assemblies being removed from Microsoft.AspNetCore.App 3.0. For more information on the motivation for this change, see Breaking changes to Microsoft.AspNetCore.App in 3.0 and A first look at changes coming in ASP.NET Core 3.0.
For more information:
https://docs.microsoft.com/en-us/aspnet/core/release-notes/aspnetcore-3.0?view=aspnetcore-3.0#assemblies-removed-from-the-aspnet-core-shared-framework
HTH. 2019-12-6 By Jacky