Entire house smells like a thrift store

About a week ago our condensation drain was clogged. HVAC guy unclogged it and put vinegar down the drain. Same day our blower had a piece of paper in it for about 12 hours. Removed the blower and took out the paper.

Air filter has been replaced, no standing water in drain pan, condensation drain working properly.

The smell is the strongest upstairs where all of our return vents are. One return vent in particular smells of a thrift store the most. When shining a camera down there, there was no visible mold or mildew.

We just had all of our ducts cleaned a few months ago as well.

Smell only really comes when AC is on.

I’m just so stressed and struggling about this, I’m not sure what to do