Project ‘ClassLibrary1.csproj’ targets ‘netstandard2.1’. It cannot be referenced by a project that targets ‘.NETFramework,Version=v4.8’ September 1, 2023 by Tarik What can I do? If your library doesn’t need the very latest features, use .net standard 2.0 in general, a library should aim to support the lowest possible version. or port your WPF app to .NET Core 3 or later