Short answer: Small appliance collection box (소형 폐가전 수거함) (rules vary by district).
Where it goes
Small appliance box소형 폐가전 수거함
Use the small appliance collection box at the 주민센터 or your apartment complex.
Five or more small appliances together can also go by free pickup (1599-0903).
Examples on the pickup list: vacuum cleaner, humidifier, fan heater, air fryer, projector.
Check your district. This item is handled differently in some cities and districts. Your building notice or district office website has the final word.