Preheat air fryer to 400°F (200°C).
Slice onions to ¼–½ inch thickness and separate into rings. Pat dry with paper towels to remove excess moisture.
Set up three bowls: one with seasoned flour (salt, pepper, paprika if using), one with beaten eggs or egg substitute thinned with milk, and one with breadcrumbs mixed with optional seasonings.
Dredge each onion ring first in the flour, shaking off excess, then dip into the egg wash, and finally press firmly into the breadcrumb mixture.
Spray both sides of each coated ring lightly with cooking oil spray and arrange them in the air fryer basket in a single layer, spaced apart.
Cook for 6-8 minutes at 400°F, flip the rings, spray lightly again, and cook for another 6-8 minutes until golden and crisp.