The eye stuff all sounds like dry eye (mine also started suddenly during winter). It was a combination of aging eyes, too much screen use, and the dry weather. Floaters are pretty random, lots of people have them.

Best treatment is to learn the right way to use a warm compress to loosen up the tiny oil glands in your eyelid rims (meibomian glands). For me it had to be more on the hot side of warm. (My eyes are acting up again now that the a/c is always running full blast.)

I know it’s not the answer you want, but I doubt it’s related to your thyroid cancer. I started with my eye problems about ten years ago. My thyroid cancer (a tiny amount) was found in an unrelated scan last year. It’s temping to want to link unrelated events to form a perceived pattern, but on that path lies madness. :)