I was having similar thoughts - find a dealer who employs technicians with a deeper understanding of A/C. That might be easier said than done: with a conventional car, there's usually a belt that turns a pulley, and the pulley has a magnetic clutch, which turns the AC compressor pump. It's pretty easy to throw up the hood and see if the compressor is turning or not. With a trained ear, you can also notice the engine RPM slowing when the magnetic clutch engages and starts turning the compressor. But the Niro uses an electrically powered A/C system and so those "conventional car" techniques won't work to diagnose a problem. The first thing I'd be checking if I had your symptoms would be the fuses.
2018 Niro PHEV Gravity Blue