Will the Xiaomi Microwave Oven work properly if the heat-resistant sticker on the oven door is broken?

Yes. The heat-resistant sticker or film on the microwave oven door is designed to withstand high temperatures and acts as a protective layer. Without the sticker, the grease and water vapour from the heating of the product will enter the door frame and seals, resulting in rust and damage to the iron mesh of the door.
Note:
The sticker issue is usually caused by microwave focusing.
It is recommended to replace the heat-resistant sticker or the oven door.