Unhandled exception. System.IO.FileNotFoundException: Could not load file or assembly 'System.Runtime, Version=7.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.

 1. Go to project root 

2. Create file name global.json

3. Paste code the below code

{

  "sdk": {

    "version": "6.0.306"

  }

}

Check out your installed list of sdks in your machine. (dotnet list --sdks)