They ‘cheat’ a little by lofting liquid water which then evaporates. We have a water softener and the cool mist humidifier left a smoke-like particulate floating in the air (i think it was either salt from the softener or minerals from the water)
We've mostly stopped using the humidifier now, because I can't find a source of distilled water that doesn't involve buying plastic bottles.
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I live in an area with very hard water (around 300ppm), and the evaporated minerals are very visible in the air (and it leaves a white residue on the surrounding area).
Tangential, but being curious how hard that was relative to mine led me to discover that Thames Water (i.e. only useful to anyone reading in London) has a pretty good page at [0] - a summary on the site itself but the PDF is really worth a look, lots of numbers. Maybe it's a regulatory requirement, but I wouldn't have expected it to be so easy to get so much information from them about my specific (it serves many districts in and around London with different sources and equipment) water supply.
[0]: https://www.thameswater.co.uk/help-and-advice/water-quality/...
Not here:
https://en.wikipedia.org/wiki/United_Kingdom_water_companies
(E.g. Canada Pension Plan, Morgan Stanley, Hong Kong based investment trust)
As I said, it may be a regulatory (Ofwat) requirement, but it isn't just a public body doing right by its citizens.
Interesting anyway, not that much of it means anything to me. Though apparently if/when I try brewing beer again I should add some magnesium. (It even lists the range that's helpful as a yeast nutrient, and above which contributes unwanted taste.)
Moved to an evaporative humidifier, my air quality appliances now operate in peace.
I grabbed an evaporative one from the local big box hardware store and zero 'smoke'. You should get some bacteriostat and you'll have to replace the paper elements every now and again, but it's way better.