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.