Preheat your air fryer to 325°F (160°C). If your air fryer requires preheating, follow the manufacturer's instructions.

In a mixing bowl, whisk together the flour, sugar, baking powder, and salt until well combined.

Add the melted butter, eggs, milk, and vanilla extract to the dry ingredients. Stir gently until just combined. Avoid overmixing; the batter should be slightly lumpy.

Gently fold in the blueberries, being careful not to crush them. Ensure they are evenly distributed throughout the batter.

In a small bowl, combine the sugar, flour, and softened butter for the streusel topping. Mix until it forms a crumbly mixture.

Line your air fryer basket or tray with muffin liners. Spoon the muffin batter evenly into the liners, filling each about two-thirds full.

Sprinkle the prepared streusel topping over each muffin for that classic Starbucks touch.

Place the muffins in the preheated air fryer basket, leaving space between them to allow for air circulation. Depending on your air fryer's size, you may need to cook them in batches.

Air fry the muffins at 325°F (160°C) for approximately 15-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Check for doneness, and adjust the cooking time if needed.

Once done, carefully remove the muffins from the air fryer and let them cool in the muffin liners for a few minutes. Then transfer them to a wire rack to cool completely before enjoying your homemade Starbucks Copycat Blueberry Muffins!