Preheat the air fryer to 400°F (200°C).
Wash and dry the broccoli thoroughly, then cut it into bite-sized florets.
In a large bowl, combine melted butter, minced garlic, salt, black pepper, and red pepper flakes if using.
Add the broccoli florets and toss until evenly coated.
Sprinkle Parmesan cheese over the broccoli and toss again to distribute evenly.
Arrange the broccoli in a single layer in the air fryer basket.
Cook the Air Fryer Broccoli for 6–8 minutes, shaking the basket halfway through cooking.
Remove once the broccoli is tender and slightly crispy around the edges.
Transfer to a serving dish and top with additional Parmesan cheese before serving.