Preheat an air fryer to 400 degrees F (200 degrees C) according to manufacturer's directions.
Pour balsamic vinegar into a microwave-safe container. Cook on high power until vinegar is reduced by half, 2 1/2 to 3 minutes. Set aside.
Combine asparagus, cherry tomatoes, olive oil, salt, and pepper in a large bowl and toss until well combined. Spread out vegetables in the air fryer basket in a single layer. You might need to cook in batches.
Cook in the air fryer until asparagus is lightly browned and the tomatoes begin to burst, about 10 minutes.
Place vegetables on a serving platter and drizzle with reduced balsamic vinegar. Sprinkle with feta cheese and serve warm.