In a large bowl, toss Brussels sprouts with olive oil, garlic, salt, pepper, and red pepper flakes if using.
Add half of the Parmesan cheese and toss to coat evenly.
Preheat air fryer to 375°F for 3 minutes.
Place Brussels sprouts in the air fryer basket in a single layer, cut side down. Work in batches if necessary.
Air fry for 12-15 minutes, shaking the basket halfway through, until Brussels sprouts are crispy and golden brown on the edges.
Transfer to a serving platter and immediately sprinkle with remaining Parmesan cheese while still hot.
Drizzle with balsamic glaze, top with bacon bits if using, and garnish with fresh parsley.
Serve warm with toothpicks for easy party snacking!