F‐Ducts are not banned. At the end of 2010 everyone was using driver operated F‐Ducts. The regulations that were changed specifically banned the use of driver movement to influence the aerodynamic performance of the car. This got rid of that generation of F‐Ducts.
What some teams are doing now is allowing air to pass into a duct when the DRS is operated. It’s completely passive, there are no moving parts and it doesn’t interact with any suspension or steering systems. Therefore, I can’t see any rule that prohibits it.