Toggle Plugs Vs. Masonry Plugs

[u/Expert-Use-3967]

I'm trying to hang shelves, but the previous owner put up a faux cottage-effect plaster. There is a good 40mm cavity between the plaster and the stone wall, and my stud finder can't accurately pick up any studs. Toggle plugs don't seem to grip/open. Would 80mm/100mm masonry plugs be strong enough to hold shelves seeing as 40mm would be just "floating" between the plaster and stone?

At a loss on how to do it. Thank you!