In a medium bowl, whisk together the eggs, milk, vanilla, sugar, and salt until smooth. Add the flour and whisk just until combined — a few small lumps are fine. Let the batter rest for 10–15 minutes at room temperature.
While the batter rests, peel and thinly slice the apple. Toss the slices in a small bowl with the cinnamon and sugar until evenly coated.
Add the butter to a 6-inch oven-safe pan or small cast iron skillet. Place the pan in the air fryer at 350°F for about 2 minutes, until the butter is melted and bubbly.
Carefully remove the pan, arrange the apple slices in a single layer over the melted butter, and immediately pour the batter on top. Do not stir.
Return the pan to the air fryer and cook at 350°F for 8–12 minutes, until the pancake is puffed, deeply golden, and set in the center.
Dust with powdered sugar, drizzle with maple syrup if desired, and serve immediately.