Preheat your air fryer to 375°F for 3 minutes.
In a large bowl, toss the halved Brussel sprouts with olive oil, garlic powder, salt, pepper, and red pepper flakes until evenly coated.
Arrange the sprouts in a single layer in the air fryer basket, cut side down. Work in batches if needed.
Air fry for 12–15 minutes, shaking the basket halfway through, until the edges are crispy and caramelized.
While the sprouts cook, whisk together balsamic vinegar, honey, and Dijon mustard in a small saucepan over medium heat. Simmer for 3–4 minutes until slightly thickened.
Transfer the cooked Brussel sprouts to a serving bowl, drizzle with the warm balsamic glaze, and toss to coat. Serve immediately.