Cannot add assemblies to .Net Core application in Visual Studio 2019

When I try to add a missing assembly to my project (for unit testing specifically) I noticed that the Assemblies tab is missing in the "Add Reference" dialog , see:

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Is this a bug or a expected behavior? If it's expected how we are supposed to add the missing assemblies.

Note that I already tried through Nuget package manager and still didn't work.

How do I add assembly reference to net core project?

One method of adding references to your library is by typing it directly in the project. json file. As you can see that we have added some references under the dependencies section as shown in the following code. Let us now save this file and you will see that references are added to your library now.

It is correct behaviour. The Assemblies tab is not available for Net Core projects. You wont be able to add assemblies from your system, because Net Core projects work with dependencies from Nuget. So, to add your references, you need to use the Nuget Package Manager instead.