I clarify:
Let’s say scientists can’t come up with solutions to global problems, AI gets out of control and turns almost everyone into paperclips during wars, and in the 2040s or 2050s, the surviving people (about a few tens of millions around the world or even less) gradually return to the level of intelligence of their distant ancestors?
I don’t see us regressing before 1820. Will just be back to your horses, carriages, and living off the land.
That still requires metal and there’s no surface deposits to support it
There’s plenty in landfills to be “mined”