Preheat a 3 ½-quart air fryer to 390ºF. Set a wire rack on a baking sheet.

In a medium bowl, whisk together the flour, ½ teaspoon each of the garlic powder, paprika, and salt, ¼ teaspoon of the black pepper, and ⅛ teaspoon of the cayenne pepper.

Pour the buttermilk into a second bowl.

In a third bowl, combine the panko breadcrumbs and the remaining 1 teaspoon each of the garlic powder, paprika, and salt, ½ teaspoon of the black pepper, and ⅛ teaspoon of the cayenne pepper. Drizzle the olive oil into the panko mixture and use your fingers to rub in the oil.

Bread the onion rings, 2 to 4 at a time: Toss the onion rings in the flour mixture and shake off any excess; then, dunk them in the buttermilk to completely coat and shake off any excess. Toss them in the panko mixture, pressing gently to adhere. Arrange the breaded onion rings on the rack on the baking sheet.

Arrange one-third of the breaded onion rings in the air fryer basket in a single layer (a little overlap is fine). Cook, gently turning halfway through, until very crunchy and browned on both sides, about 10 minutes. Lightly sprinkle the onion rings with salt, transfer to a serving plate, and repeat with the remaining two batches of onion rings. Serve with the Sriracha mayonnaise for dipping, if you like.

For the Sriracha mayonnaise (optional): In a small bowl, whisk together the mayonnaise, Sriracha, and ¼ teaspoon salt; refrigerate until ready to use.