Grease three 5¾ x 3-inch mini loaf pans thoroughly, including the corners. Preheat the air fryer to 320°F for 3 minutes.
In a large mixing bowl, whisk together the flour (reserving 1 tablespoon), sugar, baking powder, and salt.
Add the egg, milk, and vegetable oil. Stir just until the flour disappears. Do not overmix — a few lumps are fine.
Toss the blueberries with the reserved 1 tablespoon of flour, then gently fold them into the batter.
Divide the batter evenly among the prepared pans, filling each about two-thirds full.
Place the pans in the air fryer basket with space between them for airflow. Air fry at 320°F for 22 to 28 minutes.
Insert a toothpick into the center of a loaf. If it comes out with wet batter, add 5 minutes and test again. Moist crumbs are fine.
Cool in the pans for 10 minutes, then turn out onto a wire rack to cool completely before slicing.