01 - Preheat the oven to 425°F. Line two large baking sheets with parchment paper or lightly coat with nonstick spray.
02 - Separate onion slices into individual rings, discarding the very small inner rings or setting them aside for another use.
03 - Arrange three shallow bowls: combine flour, paprika, garlic powder, salt, and black pepper in the first; whisk eggs and milk together in the second; place panko breadcrumbs in the third.
04 - Dip each ring into the flour mixture, shaking off excess, then into the egg wash, and finally coat evenly with panko breadcrumbs, pressing gently to adhere.
05 - Place coated rings in a single layer on the prepared baking sheets, then drizzle or spray lightly with olive oil for enhanced crispiness.
06 - Bake for 20 to 25 minutes, turning halfway through, until the rings are golden and crispy.
07 - While baking, whisk together mayonnaise, sour cream, buttermilk, herbs, seasonings, and lemon juice until smooth; chill until serving.
08 - Serve the onion rings hot accompanied by the chilled ranch dip.