The Scenery Scanner opens a map where FlyHub can scan your installed simulator scenery packages.Use it if you want FlyHub to know which airports and scenery packages are installed on your computer.
Simulator Overlay is an in-sim overlay. It can show landing toasts and the close-flight prompt while your simulator is open.Use it if you want to finish flights without switching back to the main FlyHub window.
Stream Overlay is different from Simulator Overlay.Stream Overlay creates a local browser source for streaming software such as OBS or Streamlabs. It is for content creation and live streams.