Your project does not reference ".NETCoreApp,Version=v6.0" framework. Add a reference to ".NETCoreApp,Version=v6.0" in the "TargetFrameworks" property of your project file and then re-run NuGet restore.
Your project does not reference ".NETCoreApp,Version=v6.0" framework. Add a reference to ".NETCoreApp,Version=v6.0" in the "TargetFrameworks" property of your project file and then re-run NuGet restore.