Attempting to scaffhold into blank ASP.NET Core project(s) causes error

[marwalsch]

File a bug

I am attempting to scaffhold Identity with a Blazor Server Project. Scaffholding into the Razor template used to work two weeks ago.
Now, everytime I follow the instructions to scaffhold into Blazor Server or Razor projects I get an error as soon as I select the "New Scaffholded Item" in the solution explorer (described below).

I tried:

• repairing VS2019;
• deleting .vs folders;
• .NET 5 and .NET 3.1;
• both omitting and selecting the "Individual Accounts" option when setting authentication;

Include stack traces

An Error window pops up stating "An item with the same key has already been added."

Include provider and version information

Target framework: .NET 5 and .NET Core 3.1
Operating system: Windows 10
IDE: Visual Studio 2019 16.10.2

[marwalsch]

I'm closing as I could quite accurately pinpoint this issue actually being Visual Studio related, though I wasn't able to resolve it.