Cook macaroni in a large pot of water with the tablespoon salt until just tender and drain. Meanwhile, melt butter in a saucepan, stir in sauce flour for 1 minute and gradually whisk in milk.
Simmer for 3 minutes until thick, then remove from the heat and stir in cheddar, sauce salt and pepper. Fold in pasta, spread in a shallow container and refrigerate within 2 hours; chill for at least 4 hours until firm, additional to active prep time.
Divide the cold macaroni into 24 equal portions and press each into a firm ball roughly 1 1/2 to 1 3/4 inches across. Refrigerate the shaped balls for 20 minutes.
Put coating flour, beaten eggs and panko in separate shallow bowls. Roll each ball in flour, dip in egg and press gently into panko, covering it completely.
Preheat the air fryer to 360°F. Brush the bites lightly with the measured oil and arrange in a single uncrowded layer, working in three batches of about eight.
Air-fry each batch for 12 to 14 minutes, turning carefully halfway, until golden and 165°F in the centers. Keep uncooked coated bites refrigerated between batches.
Rest the cooked bites for 3 minutes before serving; each bite counts as one serving.
