Package 'EntityFramework 6.2.0' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'

The problem is your entity version is confused with .NetFramework and .NetCore. Your application target framework is Asp.Net Core. So You should install package related with Asp.net Core

In your case 'EntityFramework 6.2.0' is supports by .NETFramework,Version=v4.6.1' not by '.NETCoreApp,Version=v2.0'. So use this below version of entity framework instead of yours.

PM>  Install-Package Microsoft.EntityFrameworkCore -Version 2.0.1 

Alternatively you can change your target framework to net461 as below.

<TargetFramework>net461</TargetFramework>

By changing your target framework to net461 makes you available to use .net core and full .net frameworks. I think that for this period of time, this approach is better. Because EF Core still hasn't got some main features like many to many relationship and some others. Sure it depends on your needs and expectations from an ORM tool.