OK, this is just plain weird. Every so often when I try and run a new C# Windows Forms Application (this only ever seems to happen when the app is newly created and being run for the first time) I ...

As Microsoft indicated above, the Web Forms Designer with Web Live Preview, pictured below with Split (code and design) view option, was actually introduced back in July 2021 in VS 2022 Preview 2.

These include a drag-and-drop XAML designer for VS code, a more modern UI theme, expanded support for Windows Presentation Foundation (WPF) features, and full compatibility with .NET 9.