This is an optional property.
It is used only if ButtonType is TrayButtonType.PopupToggleButton
When this property is set and non-null, a Help button will be displayed in the popup header, and when clicked, opens the URI within the default browser.
If null (the default value) then the Help button will not be displayed.
Upon initially reading this DAML property, the URI string will be validated as an Absolute URI. If validation fails, then the help URI will be ignored, and no help button will be displayed.
Target Platforms: Windows 11, Windows 10