Why I Could not add Identity to project

I have problem when I am try to add Identity to my project. Somehow I get error message

So far I when I go to NuGet Packages and check for updates there is no any updates for my projects. Since I use .net core 5.0, I try also to check downgrade EntityFrameworkCore to 5.0.2 (currently 5.0.3) but still have problem.I try also to remove NuGet Packages coockies but nothing happenedAlso, I try to remove everything from

C:\Users\Anonymous\AppData\Local\Microsoft\VisualStudio\16.0_11970351\ComponentModelCache

I currently use three way aritecture and I check version on my Class Libary and it is set to .NET 5.0

I have no idea anymore what could be the problem, what ever I try there is no way to run successfull.Does anyone how what could be the problem ? What is wrong here ?