https://www.theregister.com/2021/03/15/dotnet_6_preview_2/
Microsoft has released its second preview of .NET 6, but confirmed there will be no visual designer for WinUI 3.0 when it comes out in November this year.
The register
It will be hard to work fast without seeing what the XAML will look like. Will they fix all the controls so they work with WinUI 3. Many were missing the last time i looked. It will take a long time before WinUI 3 is better than WPF.