Figma should make the mockups in the prototypes downloadable. it will save alot of trouble trying to find our own mockups
You could select each from of the prototype, then Export them from the Editor. I like a simple “Download screens of prototype” like you’re describing, but Figma (I imagine) wouldn’t want that as it takes more elements outside the software. Also, sometimes in a prototype, there’s Overlays and I’m not sure how that downloading experience might go.
Just guessing, though.