Both iOS and macOS offer the possibility to control the entire system via keyboard only. This option is called "Full Keyboard Access" and may be enabled in the Accessibility Settings (see attached screenshots). The behavior differs from the more basic Tab/Backtab navigation which is well supported by Qt.

When navigating a QML app with this feature activated, the system "only" sees the elements that are visible on the screen. Any off-screen elements are not reachable via the keyboard navigation.

See https://developer.apple.com/documentation/uikit/uikeycommand/navigating_an_app_s_user_interface_using_a_keyboard?language=objc for more information about Apple's ideas behind this.

Especially UIFocusItemContainer and UIFocusItemScrollableContainer seem relevant to this. The current change in focus may be observed with UIFocusDidUpdateNotification.