Wash the Brussels sprouts and cut off the stem and remove the outer loose leaves. Then cut them in half or quarters, if they are large. Add them to a large bowl.
Add the honey, avocado oil, balsamic vinegar, salt, pepper, and red pepper flakes to the bowl and stir well to combine.
Lay the Brussels sprouts in a single layer in the air fryer. (You may have to work in batches). Set the temperature to 400 F and the time to 8 minutes. When the timer goes off pull out the air fryer basket and turn each Brussels sprout over. Return to the air fryer for 4 more minutes.