If you set the WinUI viewer's ViewMode to PrintPreivew in the XAML or the code, the toolbar button's state and value don't change. Hence, even though the report is displayed in PrintPreview, the button for switching the ViewMode is still showing 'Switch to PrintPreview' and is not highlighted. When you click it, the report is displayed in Interactive View, the button becomes highlighted and the tooltip states 'Switch to Interactive mode'.