Preheat air fryer to 320°F for 2–3 minutes. Lightly grease silicone donut hole mold with cooking spray.
In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, and salt until combined. Sift cocoa if possible.
In a separate bowl, whisk egg, milk, melted butter, and vanilla until smooth.
Pour wet into dry. Stir gently until just combined — do NOT overmix. Fold in chocolate chips if using. Batter will be thick and scoopable.
Fill each mold cavity ¾ full using a cookie scoop or tablespoon. Do not overfill.
Place mold in air fryer. Air fry at 320°F for 7–10 minutes until a toothpick in the center comes out clean. Check at 7 minutes.
Rest in mold 2–3 minutes, then pop out onto a wire rack. Cool 3–5 minutes until warm but not hot before glazing.
Whisk glaze ingredients in a shallow bowl, adding milk 1 tsp at a time until smooth and pourable.
Toss warm donut holes in glaze or dip individually. Let excess drip off on rack. Add sprinkles immediately. Allow 5 minutes to set.
Serve warm. Best enjoyed the same day.