Unofficial.System.Windows.Forms.Legacy (nuget): This package includes types and controls that were removed from System.Windows.Forms in .NET Core 3.x / .NET 5. Specifically this includes Menu and ContextMenu which work fine as long as you don't need the Control.ContextMenu or Form.Menu properties.  The code in this package was disassembled using ILSpy from the .NET Framework 4.8 DLLs on a Windows 10 21H1 system.
Keywords: System.Windows.Forms|WinForms|Legacy|Compatibility|ContextMenu|Menu