Migrating versions in project on Visual Studio

Hi!

I'm trying to migrate a hobby project of mine into a MVC 6 project with ASP.NET Core 5 from a ASP.NET 4.6.1 MVC 5, and upon doing so I get errors from IntelliSense that ASP.NET 5 Core doesn't support, for example the ApplicationInsights package with error code CS0246. Even though I switch "project" to run the 4.6.1 version the errors persists. I haven't found a good thread on how to solve this issue, or isn't it possible at the current time? I have 92 errors in my code with this error.

Regards, Joel