extra duct

Hi! New to 2 air units and I believe the 39 mb traveler has 2 ( correct me if I’m wrong) I believe a bedroom and main area. Are the ducted together or is the one unit specific to the bedroom 1 to the living area? Also, there is 1 duct in the mid room, but it’s not near the ceiling, is there any...

Replacing the rear AC on my 2019 Elkridge and I found that in addition to the rectangular duct connections on the right and left side, there is an additional round duct on the cold air side of the plenum that goes back into the ceiling but I have no idea where it goes or what it is for. Any ideas?