Putting a couple of drops of 5% povidone iodine in the little cup area of a humidifier may have risks in addition to severe iodine allergies which should always be checked before using povidone iodine in general
There are some studies to indicate vaporizing diluted betadine may help kill MRSA and other dangerous bacteria in the respiratory track and lungs. Too much iodine is dangerous.
I do not recommend this publicly until more research is done.
I would, though, likely try this on myself if my previous COVID protocol was not enough to prevent a bronchitis or new-onset pneumonia I have not had to do this yet.