2017Kia sorento bad vinegar small coming out of vents. seems to be a problem for years.
Could well be vinegar. Leaves can get into the air vents, then decompose and if conditions are right, ferment. This makes alcohol, which then converts into vinegar.
The solve is to clean out the system. If you’re a little handy, you can remove the blower fan (generally under the glove box, mounted with 3 screws/bolts, and with an electrical cable connected to it) and feel around in there to see if there’s any plant debris.
Much beyond that and I’d recommend taking it to a shop and having a pro do it, but that can get expensive.
Sometimes a bandaid fix is to turn the fan on full blast and shoot a can of Lysol down the intake (just in front of the windshield)