No, powering a microwave oven with dark energy would not transform it into a "microwave freezer." Dark energy is a theoretical concept in physics used to explain the observed accelerating expansion of the universe. It is not a form of energy that can be harnessed or used to power appliances.
Microwave ovens use electromagnetic waves in the microwave frequency range to generate heat and cook food. They work by emitting microwaves that are absorbed by water, fats, and sugars in the food, causing them to vibrate and generate heat. Dark energy, on the other hand, is unrelated to the functioning of a microwave oven and cannot be used to alter its operation or convert it into a freezer.
A microwave freezer, as the name suggests, would refer to a device that combines the functionalities of both a microwave and a freezer. However, such a device does not currently exist in mainstream household appliances.