Nobody can solve this problem in the discussion and it's been going since July. None of us can download the application/tool we need and we all have the same problem. Please help.
I fixed the issue. If you have this problem, you should check your global.json file and make sure you reduce it from 5.0.0 to 3.1.10, because the 5.0.0 version is still in beta and does not properly support dotnet-ef yet.