global::system.runtime.versioning.targetframeworkattribute error code example

Example: Error CS0579 Duplicate 'global::System.Runtime.Versioning.TargetFrameworkAttribute' attribute MyUIApp D:\MyUIApp\obj\Debug\netcoreapp3.1\.NETCoreApp,Version=v3.1.AssemblyAttributes.cs 4 Active

Error  CS0579  Duplicate 'global::System.Runtime.Versioning.TargetFrameworkAttribute' attribute    MyUIApp
D:\MyUIApp\obj\Debug\netcoreapp3.1\.NETCoreApp,Version=v3.1.AssemblyAttributes.cs   4   Active