solution does not build when adding referencing to plugin project using steps in Microsoft How-To

To reproduce (following the steps here https://learn.microsoft.com/en-us/power-apps/developer/component-framework/import-custom-controls#create-a-plug-in-project-and-add-a-reference-to-it-in-your-solution):

> pac solution init -pn xxx -pp xxx
> pac plugin init -o Plugin
> pac solution add-reference -p Plugin
> msbuild or dotnet build or dotnet msbuild

We get the error:

C:\Users\emman.nuget\packages\microsoft.powerapps.msbuild.solution\1.21.5\build\Microsoft.PowerApps.MSBuild.Solution.targets(102,5): error : Unable to find assembly registration configuration for C:\Users\em
man\code\bin\Debug\net462\code.dll in the destination: obj\Debug\Metadata\PluginAssemblies [C:\Users\emman\code\Solution\Solution.cdsproj]

Reproduce the steps with pac solution init, pac plugin init, pac solution add-reference, and dotnet build. Start at Microsoft.PowerApps.MSBuild.Solution.targets line 102 and the generated Solution.cdsproj; done means the referenced plugin solution builds without the assembly registration error.