Preheat your air fryer to 320°F (160°C) for about 3 minutes. Place silicone muffin liners or double-layered paper liners on your work surface. If using paper liners, it is best to place them inside silicone cups or small ramekins to help them hold their shape in the air fryer.

In a medium-sized mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt. Ensure there are no large lumps so the muffins rise evenly.

In a separate small bowl, beat the egg lightly. Whisk in the milk, vegetable oil, and vanilla extract until the mixture is smooth and well combined.

Pour the wet ingredients into the dry ingredients. Use a spatula to gently fold the mixture together until just combined. Be careful not to overmix, as this can make the muffins tough. Gently fold in the blueberries.

Divide the batter evenly among the 6 prepared muffin liners. They should be about 3/4 full. This allows enough room for the muffins to rise without overflowing.

Place the muffin cups into the air fryer basket, making sure they are not touching each other so the air can circulate. Cook at 320°F (160°C) for 12 to 15 minutes. Check them at the 12-minute mark with a toothpick; it should come out clean when inserted into the center.

Carefully remove the muffins from the air fryer and let them cool on a wire rack for at least 5 minutes before eating. This helps the structure set and makes the liners easier to remove.