Heat vegetable oil in a deep fryer or large pot over medium-high heat to 350°F (175°C), ensuring there's enough oil to fully submerge the onion rings.

Whisk together all-purpose flour, garlic powder, paprika, salt, and black pepper in a medium bowl until smooth and well combined.

Pour buttermilk into a separate bowl, creating a dipping station for the onion rings.

Dip each onion ring into the buttermilk, then coat them with the flour mixture, shaking off excess.

Return the coated onion ring to the buttermilk for a second dip, then dredge in panko breadcrumbs.

Carefully place the coated onion rings in the hot oil in batches, frying for 2-3 minutes until golden brown.

Transfer the fried onion rings to a paper towel-lined plate to drain excess oil.

Allow to cool slightly before serving with your favorite dipping sauces.