DIAGNOSIS Grease and food particles get pulled up into the heating chamber and carbonize, causing smoke and burnt smells. Yeah, it's a design flaw in a lot of basket-style air fryers.
FIX Unplug and let it cool completely. Use a damp microfiber cloth wrapped around a chopstick or similar tool to gently wipe the metal heating element and the interior walls above the basket. Don't spray cleaner or water directly into the top. For tough grease, dip the cloth in a mix of warm water and a drop of dish soap, wring it out thoroughly.
IF THAT DIDN'T WORK If smoking is severe and persistent, it might be debris caught on the fan blades behind the element. You can sometimes dislodge it by turning the unit upside down and gently shaking/tapping it. Don't poke objects up there.
HEADS UP That smoking is a fire hazard if enough grease builds up. Clean the interior ceiling every few uses if you cook greasy foods. Placing a slice of bread in the basket for a few minutes on low heat can help absorb some odors after cleaning.