Preheat the air fryer to 350°F (175°C) for 3 minutes. Lightly spray the basket with cooking spray.
Separate the biscuits and cut each one into quarters. Roll each piece between your palms into a smooth ball — you will have 32 donut holes.
Stir the sugar and cinnamon together in a shallow bowl. Melt the butter in a separate small bowl.
Working in 2 batches so the basket is not crowded, arrange half the balls in a single layer with a little space between them.
Air fry for 4–5 minutes, shaking the basket halfway, until puffed and deep golden brown. Repeat with the second batch.
While warm, brush or dip each donut hole in the melted butter, then roll in the cinnamon sugar until well coated.
Serve immediately while warm and crisp.