This is mainly true. According to an article published by VeryWell Health, "microwaves utilize a type of radiation called non-ionizing radiation that is not linked to cancer." Unlike ionizing radiation that's often emitted by nuclear plants and X-rays that can cause cancer, this type of radiation has shown no link. However, the article also explains that "the exposure of certain foods to microwave radiation may create cancer-causing substances, called carcinogens." This is more of an indirect cause than a direct cause of cancer.
Can Microwaves Cause Cancer? (verywellhealth.com)
Additionally, an article published to Medical News Today, medically reviewed by Teresa Hagan Thomas, PhD, explains that guidelines given by the government require manufacturers to produce microwave ovens based on specific criteria. They need to include "safety features that contain all electromagnetic radiation within the device" and also "shielding that keeps radiation from leaking." This ensures that microwave ovens are safe and pose no cancer risk, as long as it's used safely.
What to know about microwaves and cancer (medicalnewstoday.com)