Indeed. It takes a civilisation to build an iPhone.
I don't think people appreciate that even within the highest-tech manufacturing industries there is a lot of tacit knowledge. People shake their fists about "technology transfer" to China, and before that Japan; but that's taken decades for them to reach parity. And that's with running, copyable examples and all the parts of an existing supply chain widely available. Similarly the process for making a nuclear bomb can be written in a short paper, but few countries have successfully replicated it.
"Post-collapse recovery" and "technology transfer" are the same problem, except that post-collapse recovery is cribbing from a dead example rather than a live one and in much worse circumstances.
Collapse recovery is a fun little competence fantasy to play out in your own head. Like "the rapture" for atheists. But within our lifetimes, we have to put in the work to avoid the collapse.