Which ones still use wheat?

All the ones I’ve ever seen use a mix of gluten-free starches and flours - rice flour, corn flour, tapioca, sorghum, potato starch, etc.

Edit: googling around, its apparently actually a thing, but it’s pretty rare.

It actually works in reverse: by making a dough and washing it, starch washes out and leaves gluten and the rest of the flour.

If you dry the wash water, you’re left with wheat starch, which if you’re careful enough can be gluten free. It can be added to a gluten free flour mix in the same way that you’d use corn starch and potato starch.