How do you open and manage multiple windows in MAUI?

On desktop (and iPad multi-window), call Application.Current.OpenWindow(new Window(new SomePage())) to open additional windows, and CloseWindow to close them. Application.Windows lists open windows. Mobile phones are single-window, so guard multi-window features by idiom.

var second = new Window(new ReportPage()) { Title = "Report" };
Application.Current!.OpenWindow(second);