Finely dice the onion and mince the garlic. Preheat the air fryer to 400°F for 3–5 minutes with a baking pan inside.
Add the olive oil to the hot pan, then add the onion and garlic. Stir to coat, close the air fryer, and cook for 3 minutes.
Open and stir, add the butter, and let it melt fully.
Add the quartered mushrooms, stir to coat in the butter and aromatics, then close and cook for 5 minutes.
Stir in the arborio rice and cook about 1 minute until well coated.
Pour in one-third of the warm broth, close, and cook for 5 minutes.
Add the remaining broth, lower the temperature to 350°F, and cook for 15–20 minutes, stirring once halfway through.
Rest 5 minutes with the basket closed. Fluff, garnish with parsley, and serve.