Blanch the brussels sprouts in salted boiling water ( a gallon of water + 1 tablespoon salt) for 2 minutes and immediately transfer to ice water . Drain and pat them dry with paper towels. Season with salt and black pepper then drizzle with olive oil. Toss to coat.
Preheat the air fryer to 400°F. Place seasoned brussels sprouts in the air fryer basket. Fry for 15 minutes, shaking the basket halfway through. About 2 minutes before the cooking is done, add minced garlic and stir.
Meanwhile, in a small sauce pan over medium heat, bring balsamic vinegar to a simmer. Continue to simmer until thickened and reduced by half. Remove from the heat and stir in olive oil.
Transfer cooked brussels sprouts into a large plate. Drizzle with balsamic glaze and toss to coat.