@France-Marie0 Well, I don't believe Airbnb has recognized the need for such a filter yet, so you should probably add your voice to the guests and hosts who have been requesting it, by sending them feedback on the Airbnb site. In the meantime, about all you can do is list under Eco-friendly, as it is also that, which will attract aware guests and then further make it front and center in your listing that you are EMF-free.
I'm with you on the dryer sheets- I can't understand how anyone considers them to make laundry smell "fresh" or "clean". I'm not allergic to them, they just smell horrid to me, and if I found that bedding I was given smelled of them, I'd have to be one of those "annoying" guests who asked for sheets without them- I couldn't care less if the sheets are wrinkled, just not smelling like chemicals. In fact, if I wanted to book a place, I'd likely message the host first to ask if they could accommodate that preference.
Maybe you could also market your place by taking out classified advertising space in publications which are geared to people interested in natural remedies and health. Don't know of any to specifically mention, but you probably do. In other words, find some additional places to advertise, not solely on Airbnb. You could even start a website or blog (in your spare time, haha) where other hosts who are EMF-free could list their places and simply direct interested guests to the URL of their listing on Airbnb, or other booking sites.