Cut the onions to about ½-inch thick slices for best results. Separate each slice into rings.
In a large bowl, whisk together flour, cornstarch, garlic powder, cayenne, paprika, baking powder, salt, and pepper to taste.
Reserve about ¾ cup of the flour mixture (to dust the onion rings). Set aside until ready to dip the onion.
Add eggs and beer to the bowl of the flour mixture and whisk until incorporated and the batter is smooth.
Then dip the onion ring in the dry flour mixture, shake off any excess flour, and dip it into the beer batter mixture until completely covered. Remove the onion ring and let the excess batter drip off. Coat the onion rings with breadcrumbs and place on a plate.
Preheat your air fryer to 375°F/190℃.
Spray the air fryer basket with cooking spray, arrange the onion rings in a single layer (don't overcrowd the basket), and spray them with cooking spray.
Cook until golden brown and crispy, 10-12 minutes (flip at least once for even browning).
Remove from the fryer and place on a wire rack to keep them crispy. Repeat with the remaining onion rings.
Serve with remoulade, ranch dressing, or tartar sauce, and enjoy!