My mom used to be a kindergarten and preschool teacher, and in some of her schools they sprayed products like no-burn on the curtains in the classroom. Its basically a fire retardant spray that you can apply on fabric, unfinished wood, paper, pretty much anything that’s a little porous. It leaves, like, a thin film on whatever you spray it on. Its supposedly water based and nontoxic, but I dont know if it would be laser safe. I remember one teacher saying it was just water and baking soda (which does seem possible with the film it leaves), but I dont know if that is true.
Plus side would be you could spray your material lightly and let it totally dry before lasing - so you wouldn’t need to put wet stuff in the glowforge. I’m also pretty sure you could just brush off the residue it leaves with a little effort after everything is cut. Downside, I have no idea if its laser safe and its more expensive than water.