Combine buttermilk and hot sauce in a shallow dish; mix to combine.

Combine tapioca flour, garlic salt, and 1/8 teaspoon black pepper in a resealable plastic bag and shake to combine.

Beat egg in a shallow bowl.

Mix flour, salt, brown sugar, garlic powder, paprika, onion powder, oregano, and 1/4 teaspoon black pepper in a gallon-sized resealable bag and shake to combine.

Dip chicken thighs into the prepared ingredients in the following order: buttermilk mixture, tapioca mixture, egg, and flour mixture, shaking off excess after each dipping.

Preheat an air fryer to 380 degrees F (190 degrees C). Line the air fryer basket with parchment paper.

Place coated chicken thighs in batches into the air fryer basket and fry for 10 minutes. Turn chicken thighs and fry until chicken is no longer pink in the center and the juices run clear, an additional 10 minutes.