Preheat an air fryer to 400 degrees F (200 degrees C).
Whisk together 1 tablespoon maple syrup, olive oil, salt, and pepper in a large bowl. Add Brussels sprouts and toss to coat. Arrange Brussels sprouts in a single layer in an air fryer basket without overcrowding; work in batches, if necessary. Cook for 4 minutes. Shake basket and cook until sprouts are deep golden brown and tender, 4 to 6 minutes more.
Meanwhile, whisk together mayonnaise, remaining 1 tablespoon maple syrup, and mustard in a small bowl. Toss sprouts in some of the sauce mixture and/or serve as a dipping sauce.