No, you should not put cardboard in the microwave. Cardboard is not suitable for microwave use, and attempting to do so can be hazardous.
Cardboard is made from paper pulp, which contains moisture. When exposed to the intense heat of a microwave, the moisture in the cardboard can quickly turn to steam, causing the cardboard to catch fire. This can lead to a potential fire hazard and release toxic fumes into your microwave and surrounding area.
Furthermore, cardboard may also contain adhesives, inks, and other chemicals that are not microwave-safe and can leach into your food when heated, posing a health risk.
To heat or cook food in a microwave, use microwave-safe containers made of materials like glass, ceramic, or microwave-safe plastics labeled as such. Always follow the manufacturer's instructions and guidelines to ensure safe and effective microwave use. If you're uncertain about the suitability of a particular material in the microwave, it's best to err on the side of caution and avoid using it.