Preheat the air fryer to 375°F for 3–5 minutes.
In a large bowl, combine the apples, oil, cinnamon, nutmeg, and salt. Toss until evenly coated.
Arrange the apples in a single layer in the air fryer basket. A little overlap is fine, but avoid overcrowding.
Air fry for 8–10 minutes, shaking the basket halfway through.
Cook for 2 more minutes, or until the apples are tender and lightly caramelized around the edges.
Transfer to a bowl, add the melted butter, brown sugar, and vanilla, and toss to coat.
Serve warm on their own or over oatmeal, pancakes, waffles, yogurt, cheesecake, or vanilla ice cream.