Preheat the air fryer for 5 minutes at 375 degrees F (190 degrees C).
In a large bowl, toss the brussels sprouts with olive oil, balsamic vinegar, garlic powder, sea salt, and black pepper.
Add the brussels sprouts to the air fryer basket. (Don't crowd the basket; each sprout should be touching the bottom, so cook in batches if they don't fit.) Cook for about 5 minutes.
Remove and shake the air fryer basket to toss the sprouts, then cook for another 5 minutes (or a few minutes longer for larger sprouts), until crispy and golden brown.