I have recently heard that the alpha version of .NET Core (.NET Core 3.0) supports Windows Forms and WPF. But the Visual Studio Designer (and Visual Studio) doesn\'t
If the Forms designer is missing. Try adding another Windows Form to your project. Once I did this, the Designer for my other Windows Form appeared.
If you are using Visual Studio 2019, make sure to get the latest update which includes the Windows Form Designer. Some of the earlier version do not include it.