MAUI itself does not directly implement its own FolderPicker, but it provides access to the native API so you can call the native folder pickers.
Gerald's blog and sample (referenced from his StackOverflow post that you linked) demonstrate this for both Windows and Mac.
https://blog.verslu.is/maui/folder-picker-with-dotnet-maui/
https://github.com/jfversluis/MauiFolderPickerSample