Cut the whole chicken into 10 pieces and place in a large bowl.
Sprinkle chicken with 1 teaspoon kosher salt and 1/2 teaspoon black pepper.
Pour buttermilk over chicken pieces, ensuring they are fully submerged, then refrigerate and marinate for at least 1 hour.
In a separate large bowl, whisk together 1 tablespoon kosher salt, 1/2 teaspoon black pepper, flour, garlic powder, paprika, cayenne pepper, onion powder, and ground mustard.
Preheat the air fryer to 390ºF and lightly spray air fryer racks with cooking spray to prevent sticking.
Remove chicken from buttermilk, letting excess liquid drip off, then dredge each piece in the flour mixture and shake off excess.
Arrange chicken pieces in a single layer in the air fryer basket.
Air fry for 18 to 20 minutes, flipping halfway through, until crispy, golden brown, and internal temperature reaches 165ºF.