Topic:
https://docs.elementscompiler.com/VisualStudio/Designers/
States:
WinForms, being a technology that is mostly deprecated in favor of WPF and WinRT
But the coming .Net core 3 will fully support WinForms; it is not depreciated by Microsoft in any way; it is even extended to be able to host WPF controls on it. (Number from MS: 2.4 million developers are daily building in WinForms).