You are correct that metal bowls, including stainless steel, should not be used in microwave ovens. The microwave radiation can cause sparks and potentially damage the oven or create a fire hazard.
If a stainless steel bowl is coated with plastic, it's important to note that the bowl should not be used in the microwave unless it is explicitly labeled as microwave-safe. The plastic coating must be specifically designed and approved for microwave use to ensure it does not melt, release harmful chemicals, or cause any other safety issues.
When using any container in the microwave, it's crucial to follow the manufacturer's instructions and check for specific microwave-safe labels. If there is no indication that the plastic-coated stainless steel bowl is safe for microwave use, it's best to avoid using it in the microwave oven to prevent potential hazards.