I think energy is least of problems. At the beginning forests provide a lot of energy and would be enough to bridge to industrial times (at least for us).
The real issue, I think, is lack of easily available raw materials like iron, tin, copper, etc. We have depended A LOT on iron practically lying on the ground.
Without having some iron easily available any startup civilization wouldn't know to look deeper and even if they wanted, they would not have any tools to do so.
At least with energy there is multiple ways to acquire it.
On the other hand there’s a lot of already processed and extracted iron and steel we’ve conveniently dug up and left around for future societies to maybe harvest.
Most of it is exposed to weather - which means it'll oxidize and decay to uselessness rather quickly, and eventually dissolve and become diluted. With ores, we had it all in convenient form.
A lot of it yeah but large thick things like bridges will probably survive for quite a while in usable sized chunks. Copper too will be pretty available and protected in wires. It really depends on what timescale we're talking about though in the end. If we talking about humans rebooting there could still be usable bits around depending on how long it takes to begin rebuilding. If we're talking about a whole new intelligent species I agree they'll have vanishingly little to work with.
"Ore genesis" is the term of art in geology for how various mineral ores form. Typically this involves a source, transport, and trap. Biological processes can play a major role (iron, limestone).
Useful ore deposits tend to be vast, with absoutely immense amounts (many trillions tons) of paydirt. The value of ores are that the minerals of interest are concentrated, sometimes to very high levels (50% or more of total material), though increasingly lower-grade ores (1% concentration or lower) are utilised. This means that you've got to move 99 units of mass for every unit of primary mineral extracted (overburden).
Even very large human formations are small by geological standards. The World Trade Centre towers contained about 200,000 tonnes of steel. That's a lot for humans, but a minuscule amount on a geological scale. (https://hypertextbook.com/facts/2004/EricChen.shtml)
Current iron ore extraction is on the order of about 2.5 billion tons/year. That's roughly 1/3 ton per person on Earth.
I think it still works out to a net difficulty increase to any group trying to restart an industrialized civilization because of how much easy energy reserves have been permanently extracted. There’s basically no surface level coal/oil/gas that could be tapped into and finding the remaining reserves from scratch might be prohibitively difficult.
Then there’s the question of how much of the steel will still be usable when it’s time to extract it. That’s a variable problem depending on how long the ‘dark age’ is before people are rebuilding I suppose. It could be like Doctorow’s Walkaway where there’s abundant enough discarded resources you can almost achieve post-scarcity (but that world never wen through a hard crash it was more building a parallel society than a whole new one). Or it could be centuries later when a lot of the steel will be rust. Hard to say.
I think energy is least of problems. At the beginning forests provide a lot of energy and would be enough to bridge to industrial times (at least for us).
The real issue, I think, is lack of easily available raw materials like iron, tin, copper, etc. We have depended A LOT on iron practically lying on the ground.
Without having some iron easily available any startup civilization wouldn't know to look deeper and even if they wanted, they would not have any tools to do so.
At least with energy there is multiple ways to acquire it.