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 can cook over a wood fire and teach others the same. I can do carpentry with un-powered hand tools to an acceptable level. I am a pretty decent archer. Hopefully I could find a group of survivors who valued those skills over my delicious flesh.
I wish you good luck!