Slice the sweet onion into thick rings and separate them carefully.
In a medium bowl, whisk together the whole wheat flour, unflavored whey protein, garlic powder, smoked paprika, sea salt, and black pepper.
In a separate bowl, lightly beat the egg whites until frothy, then slowly stir in the light beer.
Gradually whisk the wet egg and beer mixture into the dry ingredients until a smooth, thick batter forms.
Dip each onion ring into the batter, ensuring it is fully and evenly coated.
Place the coated rings in a single layer in an air fryer basket, working in batches if necessary to avoid overcrowding.
Air fry at 375°F for 10-12 minutes, flipping the rings halfway through, until the coating is golden brown and crispy.
While the onion rings cook, whisk together the nonfat Greek yogurt, lemon juice, and hot sauce in a small bowl to create the dipping sauce.
Serve the hot onion rings immediately with the chilled yogurt sauce on the side.