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?
A fun example of that, there’s been time and again where prototypes of things we now think of as modern were made thousands of years before. But they didn’t have the prerequisite tools and information to make it anything more than a prototype.
Like “Hero’s Engine”, a thousand of years old toy that’s a fully working Bronze Steam Engine, but it’s basically like 10cm in size. But cause they weren’t good enough at metallurgy yet, they knew it could work bigger but didn’t have any methods to make it bigger (copper and bronze can’t handle the strain that anything bigger than that would make, and that’s all they knew how to use at the time)