It’s easy. You have .NET Framework 4.8 which is followed by netcore 3.1 which is followed by .NET 5 and now 6. 4.8 supports netstandard 2, core and 5 additionally support netstandard 2.1. You can then use ASP.NET with 4.8 or ASP.NET Core with 3.1 onward. Entity Framework is only supported on 4.8 and Entity Framework Core up to 3.1 support netstandard 2 so .NET 4.8 and 3.1 onwards both. But the versions after 3.1 (obviously they went to 5 there) only support netstandard 2.1 so only dot net core 3.1 and onwards.

Perfectly clear and reasonable.