NuGet Warning NU1211
Project
DotnelToolReferenceProject.csproj
must have a single package reference(s).
Issue
The project you are attempting to restore has special restrictions and exactly 1 PackageReference package must be specified.
Solution
Projects of this style are normally not ordinary projects and the dotnet tool commands should be used to manage your dotnet tools. Alternatively, change your project to specify exactly 1 package.