Preheat the air fryer to 375F (190C) without the trays.
Slice the bread slices into 3 to 4 vertical pieces (sticks).
In a small dish, combine ½ teaspoon cinnamon and 2 teaspoons sugar and set aside.
In a 9x13 baking dish, whisk the eggs. Add the milk, vanilla, and remaining ½ teaspoon of cinnamon and whisk to combine.
Place the bread stick slices in the baking dish and let the first side soak up the egg mixture for 15 seconds per side. TIP: soak as many bread "sticks" at one time as you can fit inside your air fryer.
Cook:
Spread a little butter on the hot air fryer basket or spray it with cooking spray. Do this after it's done preheating. Place the soaked French toast sticks in the preheated air fryer, working in batches if necessary, apart so they don't touch.
Cook at 370F (190C) for approximately a total of 6 minutes, flipping the slices over after 3 minutes and cooking the second side for another 2 to 3 minutes, depending on the thickness of the bread used. You'll know they are ready when the second side is golden brown, and the middles have puffed up (this means they're cooked through).
Serve:
Remove the French toast sticks from the air fryer and sprinkle them with some of the cinnamon sugar.