Technically, it is possible to create a device that uses an electric heater to generate heat and cook food, but it would not be a traditional microwave oven. A microwave oven operates by using electromagnetic waves, specifically microwaves, which are generated by a magnetron. These microwaves cause water molecules in the food to vibrate, generating heat and cooking the food from the inside out.
Using an electric heater instead of a magnetron would essentially create a small conventional oven or a toaster oven, which uses heating elements to generate heat. It would not have the same rapid cooking capabilities or even cooking performance as a microwave oven.
While you could create a heating device with electric heaters, it wouldn't be a direct replacement for a microwave oven. It would be less efficient at heating food quickly, and the cooking process would be different. Additionally, without the specific design and safety features of a microwave oven, it might not be safe to use certain containers or materials in this makeshift setup.
If you are looking for an alternative to a microwave oven without a magnetron, consider using a toaster oven or a conventional oven. These appliances can efficiently cook a variety of foods and are safer and more suitable for conventional cooking methods.