Keep in mind there is not a lot of Teflon in humidifiers most are more metal and plastic but if you’re not sure check with the manufacturer.
While most studies indicate that PTFEs & PFOAs offgas at temperatures above 500 degrees Fahrenheit, there is information that some formulations will offg as between 360 degrees and 450 degrees Fahrenheit. I don’t think Teflon is your problem with a humidifier.
The problem with humidifiers is allowing mold to grow on the filter and then mold gets spewed out with the moist air causing problems like Aspergillosis which is a the disease of the lungs that birds get caused by fungus which is found most everywhere in the environment.
Humidifiers form the the perfect storm for the production and transmission of Aspergillosis because it loves warm moist environments and were not talking about Jamaica.
Usually it’s not harmful to birds unless the birds immune system is compromised by things like bacterial infections of the mouth from drinking poop water, brooding activities like egg laying and feather molting which all three of which can occur can occur simultaneously as we learned from our cockatiel Popcorn.
All three of those issues reduce the birds immune system which then puts the bird in harms way for fungal infection. Which begs the question how do you know if your bird has Aspergillosis?
Heavy breathing, a loss of appetite and lots of drinking and pooping of a bluish coloration of mucus are signs of acute Aspergillosis which can and does lead to death
Chronic Aspergillosis is harder to detect because the symptoms might not manifest themselves to rapidly. The fungal spores flow through the birds complete system via bloodstream and then most of the major organs will get affected.
This is a disease it’s very hard to detect even for a veterinarian. It can be treated with surgery to remove easy to reach lesions and there are antifungal drugs available.
So getting back to your original question – Make sure your humidifier is sized proportionately for the room home or apartment it’s going in. More importantly use an additive to eliminate fungus and watch the filter for any discoloration – like fungal spores and replace the filter immediately if any are spotted.
Naturally paying attention to your cage birds keeper’s to do list which is making sure food and water are clean the newspaper in the cage is changed regularly and all the toys, perches and accessories are cleaned thoroughly once a month with an enzymatic cleaner like poop off and bird safe sanitizer like Pet Focus or a handheld steamer
Hope that helps