In another large bowl, whisk together the flour, salt, paprika, pepper, garlic powder, and onion powder. Take a mushroom from the buttermilk mixture and toss it in the flour mixture. Shake off the excess flour, then dunk it back into the buttermilk mixture, and then again in the flour mixture. Set aside on the prepared baking sheet in a single layer or on a plate if using the air fryer. repeat with the remaining mushrooms, giving each a double coating.