Preheat the air fryer using the preheat function or by heating it at 400°F (204°C) for 3 minutes.
Add the brussels sprouts to a large bowl with the olive oil, salt, garlic powder, and pepper. Toss to combine.
Add the brussels sprouts to the air fryer in a single layer.
Cook at 400°F (204°C) for 7 minutes. Then shake the air fryer basket to turn the brussels and cook for an additional 5-7 minutes, or the brussels are fork tender and the outer leaves are dark brown.