Seriuoosly cancer does not work like that most of the time. As in the really rare cases of spontaneous remission.
We don't actually know that. We know that thyroid cancer that gets bad enough to be symptomatic doesn't just go away spontaneously. We have no idea what percentage of cases detected in intensive screening will just go away because intensive screening is rare. We don't know how many of the positives are false.
We have much better data on breast cancer screening. The big surprise there was that 20% of the detected (but asymptomatic) cancers do spontaneously regress.
That may or may not be the same for thyroid cancer. We better figure that out fast or a lot of kids will get a lot of unnecessary procedures done on them and will end up on replacement therapy for life.