Preheat air fryer to 400° according to manufacturer's directions. Line bottom of air fryer basket with foil. Place popcorn kernels on foil in a single layer. Air-fry 5 to 6 minutes or until kernels are popped. Transfer 4 cups popcorn to medium heat-resistant bowl. Discard unpopped kernels.

Combine brown sugar, butter, and corn syrup in small skillet. Bring to a boil, stirring constantly. Remove from heat; stir in vanilla. Immediately pour over popcorn; stir to coat.

Preheat air fryer to 300° according to manufacturer's directions. Line bottom of air fryer basket with clean foil; spray with nonstick spray and set aside.

Transfer coated popcorn to prepared air fryer basket. Close air fryer and air-fry 10 to 11 minutes or until golden brown, tossing coated popcorn with tongs every 2 to 3 minutes. Remove from air fryer and carefully spread on sheet of foil or heat-resistant tray. Cool completely.