Separate the refrigerated biscuits and cut each biscuit into 3 or 4 equal pieces. Roll every piece between your palms into a smooth ball, pinching and sealing any seams so the dough stays together during cooking.

Lightly spray the air-fryer basket with nonstick spray. Arrange the dough balls in a single layer with space between them, working in batches if needed.

Air-fry at 350°F/175°C for about 5 to 8 minutes, turning the pieces or shaking the basket halfway through. Remove them when they are puffed and lightly golden, checking early because air fryers and dough-piece sizes vary.

Immediately brush or toss the warm donut holes with the melted butter. Combine the granulated sugar and cinnamon in a bowl, then roll the buttered donut holes in the mixture until well coated.

Serve the cinnamon-sugar donut holes warm. For a glazed version, whisk the powdered sugar with 1 to 2 tablespoons of milk, cool the donut holes briefly, and drizzle or toss them with the glaze.