In a typical microwave oven, it is not possible to see the food being heated while the microwave is operating. This is because the microwave's cooking chamber is designed to contain the microwave radiation and prevent it from escaping. The door of the microwave is made of a mesh or screen that blocks the microwaves from leaving the oven, but allows visible light to pass through.
However, when you open the microwave door while it is operating, you may be able to see some visual effects caused by the microwaves. Inside the oven, you might observe a faint glow or illumination around the food or on the interior walls of the microwave. This glow is caused by the interaction of the microwaves with any moisture or particles present in the food or inside the oven.
It's important to note that microwaves themselves are not visible to the human eye because they fall outside the visible light spectrum. Microwaves have a longer wavelength than visible light, which is why we cannot perceive them directly. The visible effects you might observe are secondary effects caused by the interaction of the microwaves with the food and the materials inside the oven.