It's probably not ducted to the exterior at all. Most townhouses and condos don't allow alteration of the exterior to exit a vent. It's probably dumping out somewhere in the ceiling joist, which would be BAD. That's is a fire hazard. If it is done as non externally vented, then it needs the recirculation kit. And you need to be on board with weekly cleaning of the grease filter mechanism and quarterly to semiannually changes to the charcoal filter.

Thank you Sophie Wheeler for your comment. I am very confused right now, as there's exterior wall vent(picture attached) and duct from the previous owner. Is there any other way to confirm whether or not the range hood is properly vented? How can we fix this problem?? Many thanks

Contact a local HVAC specialist. The V is for ventilation. If the fan is exhausting properly, then it just may not be strong enough. Or, it may need Makeup Air, in order to exhaust properly. Or, you may have air infiltration from the exterior into your upstairs. That is where an energy audit with a blower door test can pinpoint leaks in your building envelope.

Maybe you can try turning on your range hood to highest power then try to feel the exhaust outside your house and see if there's airflow. Also when you're cooking greasy food that produces a lot of smoke, turn your range hood to highest power.

I have contacted the energy audit will have the blower door test done. Thank you very much.