Pat the chicken thighs thoroughly dry with paper towels. This step is crucial for crispy skin. Season both sides lightly with extra sea salt and black pepper.

In a small bowl, combine the softened unsalted butter, minced garlic, dried thyme, crushed dried rosemary, dried oregano, smoked paprika, onion powder, and the optional apple cider vinegar or lemon juice. Mix well with a fork until all ingredients are thoroughly combined into a fragrant paste.

Carefully loosen the skin on each chicken thigh without completely detaching it. Gently spread about half of the garlic herb butter mixture evenly under the skin of each thigh. This infuses the meat directly with flavor and keeps it moist. Rub the remaining butter mixture over the top of the skin and flesh of the thighs, ensuring an even coating.

Preheat your air fryer to 375°F (190°C) for 5 minutes. Place the chicken thighs skin-side up in a single layer in the air fryer basket. Do not overcrowd; cook in batches if necessary to allow proper air circulation for crispiness.

Cook for 20-25 minutes, or until the internal temperature of the chicken reaches 165°F (74°C) when measured with a meat thermometer, and the skin is deeply golden brown and crispy. For extra crispiness, you may increase the temperature to 400°F (200°C) for the last 3-5 minutes, watching closely to prevent burning.

Carefully remove the cooked chicken thighs from the air fryer and let them rest on a cutting board or plate for 5-10 minutes before serving. This allows the juices to redistribute, ensuring the chicken remains moist and tender. Garnish with fresh chopped parsley, if desired.