Slice onions into 1/2-inch thick rings and separate them. You want nice, thick rings for this recipe. Set aside the smaller inner rings for another use.
Set up your breading station with three shallow bowls. In the first bowl, mix flour, paprika, garlic powder, onion powder, 1/2 teaspoon salt, black pepper, and cayenne if using.
In the second bowl, whisk together eggs and buttermilk until smooth and well combined.
In the third bowl, mix together panko breadcrumbs, regular breadcrumbs, and remaining 1/2 teaspoon salt.
Working with one ring at a time, dredge in flour mixture, shaking off excess. Dip in egg mixture, letting excess drip off. Finally, coat thoroughly in breadcrumb mixture, pressing gently to adhere. Place on a plate or baking sheet.
Preheat air fryer to 400°F for 3 minutes. Spray the basket generously with cooking spray.
Arrange onion rings in a single layer in the air fryer basket (don't overcrowd – work in batches). Spray the tops generously with cooking spray.
Air fry for 8-10 minutes, flipping halfway through and spraying again with cooking spray, until golden brown and crispy. Serve immediately with ranch dressing, ketchup, or your favorite dipping sauce.