Will subclinical hypothyroidism turn into hypothyroidism? Why some doctors prefer not to treat subclinical hypothyroidism? Is the treatment bad?

Multiple choice?? Sub clinical hypothyroidism will turn into hypothyroidism in a number of cases. Treating is not bad or dangerous. We just need to have the clinical findings, symptoms and findings to make the numbers fit the patient, not the other way around.
Support thyroid. You can take iodine orally 13.8 mg per day which will support thyroid there are otc medications that can help like biotics gta forte - sometimes thyroid meds can speed heart cause palpitations so we are cautious.
Subclinical is hypoT. Hypothyroidism can be primary - caused by a weak thyroid gland or secondary to other hormonal problems, like a pituitary problem. Or your thyroid can become dysfunctional secondary to high insulin, estrogen or cortisol. If you have functional hypothyroidism, this problem can go undetected by routine screening tests. More extensive testing can often reveal abonormalities. This is very common.