If you accidentally ran your microwave oven empty for 3 minutes and noticed a burning smell, it is possible that the magnetron, which is the component responsible for producing microwave radiation, may have been damaged due to the lack of food or liquid to absorb the energy.
Using a microwave oven that has been damaged can be unsafe, as it can potentially pose risks such as electrical malfunctions or even fire hazards. Therefore, it is advisable to exercise caution and have your microwave oven inspected by a professional before using it again.
Consider contacting the manufacturer or a qualified appliance repair service to assess the condition of your microwave and determine if any repairs or replacements are necessary. They will be able to provide you with the most accurate information and guidance based on the specific model and condition of your microwave.