I would right click on my solution file and open it with notepad. You can double check more than one project is not listed. Also it could not hurt to delete the hidden .vs folder in your solutions directory
Microsoft Toolkit installation cannot be done

Lloyd Sheen
1,076
Reputation points
So I have a new dev pc. I have copied all my source projects to the new pc and are trying to get several projects working or just executing apps from it that I use.
My WPF app tells me that I need to install the Microsoft.Toolkit.Wpf. I have seen many posts from MS telling me how to do it and well none of them work.
Using the package manager console with "dotnet add package Microsoft.Web.WebView2 --version 1.0.1418.22" tells me that I have more than one project in my solution and of course the solution has one project so this is useless.
At present I am stuck with this.