Who can inspect my home’s ductwork?

I have my AC unit inspected by a HVAC professional and he told me the unit is running fine. Only problem is the humidity level is 65-75%. My house (2800-3000 square feet, high ceilings) was built in the mid-70s with no return ducts in the upstairs bedrooms. Only 1 return duct upstairs in the hallway. The ductwork was never sealed and I assume this needs to be done. Believe there is air loss as well.

Had an air duct cleaning company come and said they would not do the cleaning unless the air ducts were sealed and provided me a quote of $3200-4000.

Are there any specialists that can fully examine the ductwork in my house to include testing via instruments via air flow, air loss, with videos analysis, etc.

Thank you!