Can I use Entity Framework 6 (not core) in .Net Core?

Surprisingly yes, if you plan to upgrade to .NET Core 3! EF6 will be updated to work on .NET Core 3.0, to provide a simple path forward for existing applications using EF6. But MS don’t plan to add any major new features to EF6. EF Core will be extended with new features and will remain the recommended data stack for all types of new applications.