Pat the chicken thighs thoroughly dry with paper towels and place them in a large bowl.
Sprinkle the chicken with sea salt, black pepper, and grated Parmesan.
Toss until the thighs are evenly coated with the seasonings.
Arrange the chicken thighs in the air fryer cooking basket or tray in a single layer, skin-side down. Follow your air fryer's instructions regarding the required basket or insert.
Divide the garlic butter over the chicken.
Air fry at 400°F (204°C) for 13 minutes.
Carefully open the air fryer and use tongs to turn the chicken, coating both sides with the melted garlic butter.
Arrange the Air Fryer Chicken Thighs skin-side up.
Continue air frying at 400°F for approximately 11–12 minutes, or until the skin is golden and crisp.
Check the thickest part of each thigh with an instant-read thermometer without touching the bone. The chicken must reach at least 165°F (74°C).
Cook for additional time if necessary, since cooking time varies depending on the size of the thighs and air fryer model.
Allow the chicken to rest for several minutes.
Garnish with parsley, green onions, or chives if desired, then serve warm.