Preheat the air fryer to 370°F for 3 minutes. Set a wire rack beside the breading station.
Separate onion slices into sturdy rings and blot the surfaces dry.
Mix flour with paprika, garlic powder, half the salt and pepper. Whisk eggs with milk. Mix panko, Parmesan and remaining salt.
Coat each ring in flour, then egg, then panko. Press crumbs firmly onto both sides and rest on the rack for 5 minutes.
Mist both sides with oil. Arrange in one layer and cook 5 minutes, turn gently, mist dry spots and cook 3 to 5 minutes more.
Remove when deeply golden and the onion is tender. Season lightly while hot.