Whether you are air frying, roasting, or baking eggplant, it should be cooked at a high temperature for a shorter duration rather than a low temperature for a longer duration. This is to get the eggplant as firm and crisp as possible. If it's cooked at a lower temperature it will steam and become very soft. Most air fryers only go up to 400 degrees Fahrenheit (204 degrees Celsius), so you should air fry eggplant at this temperature. If your air fryer goes higher than this, you can safely go up to 450 degrees Fahrenheit or 232 degrees Celsius (but shorten the cook time by a few minutes).