For those looking for solutions, no need to bother with dummy AI controllers or making a custom movement component anymore, there is “Requires Controller for Inputs” boolean flag in the new ChaosVehicleMovementComponent.
Once you unpossess and want to update the input values though, you might either want to add delay node (if quick and dirty) or some check for whether if a driver is still present in your car’s input events, because the InputActions will also fire their “completed” events after the unpossession.