Prepare the chicken: Pat the chicken thighs thoroughly dry with paper towels. Trim any large pieces of excess fat if necessary.
Make the garlic butter: In a small bowl, combine the softened butter, minced garlic, paprika, Italian seasoning, salt, and black pepper. Add red pepper flakes or lemon zest if using.
Coat the chicken: Rub the garlic butter mixture evenly over each chicken thigh. For skin-on thighs, gently place some of the butter underneath the skin as well.
Preheat the air fryer: Preheat your air fryer to 375°F (190°C) if your model recommends preheating.
Arrange the chicken: Place the chicken thighs in the air fryer basket in a single layer, skin-side up. Leave space between the pieces so the hot air can circulate.
Air fry: Cook for approximately 18–25 minutes, depending on the size of the thighs and your air fryer. Turn the chicken halfway through cooking if needed for even browning.
Check the temperature: Insert an instant-read thermometer into the thickest part of each thigh, avoiding the bone. The chicken is ready when it reaches at least 165°F (74°C).
Rest the chicken: Transfer the cooked chicken to a plate and let it rest for about 5 minutes before serving.
Garnish and serve: Sprinkle with fresh parsley and, if desired, a little fresh lemon juice. Serve immediately with your favorite vegetables, potatoes, rice, or salad.