The Windows Forms out-of-process designer is currently available as a preview Visual Studio feature in Visual Studio 2019 or later. It can be enabled in Tools -> Options -> Environment -> Preview Features dialog by checking the Use the preview Windows Forms out-of-process designer for .NET apps checkbox. Releases of .NET Windows Forms Designer are tied to Visual Studio Preview releases, so update to the latest Visual Studio Preview version to get the newest designer features.
❗ The latest designer feature shipped in Visual Studio 2022 v17.5 Preview 3 is Modernization of code-behind generation.
For the latest news on the designer please refer to the series of blogs: