Bad smell from AC

My 2009 Honda Fit was parked for a few months this year. Now when I use the AC, there is a bad smell. It doesn’t smell like any mold that I’ve smelled before (although I know molds can have many different smells). I’m not sure if it is coolant. I could see how one would consider it a sweet smell, but I’m really not sure.

If I blow air (without AC) whether it is cold or hot, the air doesn’t have the smell. Only when I turn on the AC. Unfortunately, stupid Honda made it so whenever you blow air up to the windshield, it uses the AC without cooling. So the smell is also there when I blow the air up to the windshield (even without manually turning on the AC). If I turn on the AC, then it the smell is there regardless of where I blow the air.

The AC works very well.

I checked the coolant, and the radiator is completely full and the overflow is right in between min and max. I don’t know where it was a few months ago, but to me this shows it is either a slow leak or not leaking at all.

I’ve checked inside and under the car and I don’t see any signs of a leak. The carpets in the car are completely dry.

Replacing the heater core is quite the large job, so I’m hoping to be totally sure before I go down that route. Any idea how I could confirm if it is this or mold or something else?

Edit: checked the cabin air filter and it looks fine