In a small bowl, combine buttermilk (or milk mixed with lemon juice) and let it sit for about 5 minutes.

Peel the sweet onions and slice off the tops and bottoms. Make vertical cuts around the onion, about 1/2 inch deep, ensuring not to cut all the way through.

In a separate bowl, whisk together the flour, paprika, garlic powder, onion powder, cayenne pepper, salt, and pepper.

Dip each onion into the buttermilk mixture, then roll in the seasoned flour mixture to coat.

Preheat your air fryer to 380°F (190°C) for about 5 minutes.

Carefully place the coated onions in the air fryer basket in a single layer.

Lightly spray or brush the tops with cooking spray or oil and air fry for 10-12 minutes, shaking the basket halfway through.

While the onions are frying, mix together mayonnaise, ketchup, horseradish sauce, lemon juice, and seasonings for the dipping sauce.

Once crispy and golden brown, remove from the air fryer and serve warm with the dipping sauce.