Line a tray with parchment paper or set out a wire rack.
In a shallow bowl, whisk together the sugar and cinnamon and set aside.
In a small saucepan, add your apple cider and whisk over medium-high heat until it reduces slightly. Set aside.
Separate your biscuits and use the lid of a water bottle or soda bottle to cut out the middle of each biscuit.
Place a parchment round in the air fryer basket, or lightly spray the basket with cooking spray.
Place 4 donuts in a single layer in the air fryer. Do not let them touch; if they do, remove one.
Air-fry at 350 for 3 minutes, flip, and air-fry for another 3 minutes.
Remove the doughnuts from the air fryer to the prepared sheet and repeat with the remaining biscuits.
Brush both sides of the doughnuts with the apple cider, then immediately toss them in the cinnamon sugar, making sure every bit is covered.
Serve!