Vents before cabin air filters were filthy. When starting a car, dust flying out of the dash was normal, and bugs and smoker tar&ash cycled through the system unfiltered. I removed such vents and filled them with engine degreasing detergent; soap, boiling water, household cleaner, citrus degreaser, nothing else worked. I kinda want to try cutting a furnace filter and slipping it in.
Most car airfilters aren't ideal. They aren't HEPA, there's usually no activated carbon, and sometimes they pack them with bakingsoda. Still, it's great for allergies and HVAC efficiency. Activated carbon will remove some odours and VOCs etc. It's hard to imagine a car taking in anything without filtration, but oil filters were once a novel invention.