Preheat the air fryer to 370°F. In a shallow bowl, whisk together the sugar, eggs, milk, and vanilla.
Line the air fryer with parchment paper. Quickly dip one slice of bread into the egg mixture, making sure both sides are evenly coated, and immediately transfer the bread to the air fryer. Repeat with as many slices as the air fryer will allow, without the slices touching.
Cook for 8-10 minutes, flipping halfway through, until lightly browned on both sides.
Sprinkle with powdered sugar and serve immediately with syrup. Repeat with any remaining slices.
Tip: To serve all the french toast at the same time, keep the finished slices in a warm oven until ready to serve.