Duct cleaning is a scam. If you’ve changed all the filters, the smell is probably just from the air circulating in your rooms and not from the HVAC system.

Have you wiped down every surface with eventual purpose cleaner? Make sure to get the high horizontal surfaces - the tops of doors, windows and cabinets - as well as the walls and doors below snout level.

If there is any carpet, replace it. If there are any existing window treatments, have them cleaned or replaced.

There is a slight smell in our forced air system with heat/AC is on. Hard to describe but kind of like a dog smell. Never had that issue with the last house. The prior owners had a dog and cat, but we've been here for a few years already. Anyone had luck with getting their ducts/vents cleaned? The EPA website seems to suggest duct cleaning is a scam, so that's why I've never tried it. We got new furnaces a few months ago, but still have the same smell.