The square opening on the passenger side is the fresh air intake to the HVAC. You could calk around the outside dig it is missing, cracked etc. The oblong hole in the middle is the drain that gets clogged. There is no screen or trap to stop debris from entering. You just keep an eye on it or clean it occasionally.
Re looking at the initial pics on a larger screen leads me to determine that is your AC drain. Mine does not have a hose, more like an open ended nub. When your defrost or AC pulls humidity out of the air that liquid drains out there. And if blocked, you will get a mildew smell inside and a wet floor on the passenger side when the defrost or AC is running.