Microwaves don't typically have a "stealth mode" for late-night heating because the noise produced by the appliance is primarily caused by the mechanical components involved in the cooking process, such as the rotating plate and the fan. These components are essential for even cooking and heat distribution.
While it might be desirable to have a quieter microwave for late-night use, it would be challenging to eliminate all noise without compromising the functionality of the microwave. Attempts to make microwaves quieter could result in reduced cooking performance or inefficient heating, which would be undesirable for users.
That being said, some modern microwave models have incorporated noise reduction technologies to minimize the sound produced during operation. These technologies aim to reduce the noise without compromising cooking performance. So, if a quieter operation is a priority for you, it's worth exploring microwave models that feature noise reduction mechanisms or searching for specific brands known for producing quieter appliances.
In the meantime, if you're concerned about disturbing others during late-night microwave use, you can consider placing a soft cloth or towel under the microwave to absorb some of the vibration and reduce noise transmission. Additionally, you can try to minimize the heating time or use microwave-safe containers with lids to contain noise and steam.