Maintaining a high-tech economy requires a lot of people.
I like to think I'm a smart guy. I develop software for a living. So suppose I tried to redevelop technology from scratch. I have a basic understanding of how computers work. Could I "re-invent" the computer? Not likely. I know computer chips are made from silicon and germanium. We get silicon from sand. Cool. How do you turn sand into usable silicon? I haven't the vaguest idea. Where do we get germanium? What does raw germanium in nature look like? I have no idea. Okay, skip to something simpler: We'll need wires. How do you make wire? I don't know. Most wire is made from copper. So we'll have to mine copper ore. What does copper ore look like, and where do you find it? I haven't a clue.
I suspect most intelligent people would be in the same boat that I am. We know a lot about some narrow field. But making that work requires lots of other moving parts, and we know little or nothing about most of them.
And not to be insulting, but most human beings aren't smart enough to build advanced technology. Even with detailed instructions, many couldn't manage it. I've worked in tech support, trust me on this.
If just the right books survived, I presume smart people could figure it out. I suppose that if I knew the apocalypse was coming and I was given access to any experts I needed, I could put together books telling someone how to build various technology, step by step, from zero. Here's where to look for copper ore. Here's what it looks like. Here's how to dig it out and refine it. Here's how to make it into wire. Here's how to make insulation. Etc. up to here's how to assemble all these parts to make a power plant. I'm sure there are books out there on all the pieces of this. But someone trying to rebuild would have to find all those books and read them and understand them and pull it all together. I think that would be very hard.
In a post-apocalyptic world with a greatly reduced population, I think there would be many communities with someone who is an expert electrician ... but who has no idea where to get wire and switches. Another community might have a great miner ... but he has no idea how to refine the metals once mined. Etc. There would be lots of people who know how to do step 7 in some task, but there's no one around who knows how to do step 6 or step 8. Or someone might know how to do a step if only he had the right tools, which he doesn't, because he doesn't know how to make the tools.