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
Although the official WPF GitHub Repository states that:
Note: The WPF visual designer is not yet available and will be part of a Visual Studio 2019 update.
There is this example video in which the visual designer is being used.
Hope it helps!