Just looked it up because of your comment. Plackers contain PFAS in the form of PTFE (Teflon). I play with those in my mouth all the time. Holy cow.
Not that that same risk applies to dental floss (I don't think many people heat their dental floss to a few hundred degrees), but your statement was more general than that.
So "the most nontoxic" is pretty darn accurate. PTFE is substantially less toxic than air, water, table salt, cellulose, polypropylene, or pretty much anything else you're likely to put in your mouth.
If you tried that with oil you would have an enormous cloud of smoke - and the smoke from the oil is MORE toxic than the smoke from the PTFE.
So yah, the most nontoxic is completely correct.
And BTW, it is far safer for your birds to use PTFE cookware vs oil because you would have to get the PTFE much hotter vs the oil for there to be any issue.
I don't think it's necessarily true that cooking with PTFE is safer, even if the smoke is more toxic to birds, because the PTFE fumes are invisible, so you can kill your birds before you realize that there's a problem. It's not likely but it's possible.
I also don't think it's really true that you have to heat PTFE "to almost glowing". WP says PTFE starts to decompose around 350 degrees (science) and is already a health problem for birds above 250 degrees, killing parakeets at 280 degrees (after four hours of exposure, which was longer than it took burning butter fumes to kill the parakeets). See https://en.wikipedia.org/wiki/Polytetrafluoroethylene#Safety. Things don't start to glow until about 525 degrees, or a little hotter if they're very white.
The difference between 280 degrees and 525 degrees is even bigger than it sounds in terms of heat input. It's 145 degrees, yes, but at those temperatures radiation (in the infrared) is the dominant form of heat transfer, and radiation is proportional to the fourth power of temperature; at 280 degrees blackbody radiation is 5300 watts per square meter, while to get something up to 525 degrees you have to pump in 23000 watts per square meter, more than a factor of four.
The summary is that it takes four times as much heat per minute to make your teflon skillet glow as it takes to heat it up enough to kill your parakeet in four hours, which is about the same temperature that soybean oil starts smoking at, so if you have birds you might want to think about switching to cast iron, or at least always using abundant oil on your teflon so you're guaranteed to notice if you go outside the safe temperature region.
None of this is relevant to bike chain lube or dental floss.
PTFE is completely safe.
Microplastics of PTFE, particularly fibers, provoke the same sort of response as similar asbestos, for the same reasons. A smooth PTFE surface, e.g. in a surgical implant, evokes a completely different response.
So, no: PTFE can be safe, but is not necessarily. Convexity matters.
PTFE is soft and not sharp, completely the opposite of asbestos which is both needle sharp and very hard and stiff.
Not to mention no one is making microfibers of PTFE, the fibers are much larger that that.
The principle, as I recall, is that when a nanoparticle or nanofiber lodges somewhere, poking a membrane or anyway intruding, immune system cells attack it with increasingly caustic chemicals, trying to break it down. If it is too stable, they fail, but don't give up. It is this inflammatory response that underlies asbestos's toxicity.
A smooth, locally flat surface does not, by itself, provoke that immune response, and chemically PTFE doesn't draw attention. But PTFE happily adopts any shape. So, maybe nobody makes PTFE microfibers or nanoparticles on purpose, but that doesn't mean there aren't any.
The short story is that tests showing PTFE surgical implants don't evoke an inflammatory response do not tell you much about effects of PTFE in different circumstances. Likewise: people can wear metal jewelry for years, but that doesn't mean you can poke a knife through somebody with no effect.
There was a recent report that those mesh tetrahedral tea bags each release literally billions of plastic nanoparticles into your tea. That cannot have been deliberate. I wonder if those have been banned or recalled yet...