I honestly don’t think it’s that bad. Wood has a pretty big ROI. It’s not even underground, you just chop it down. But it’s also not hard to accidentally cut down all your trees on your island or whatever. As long as you can maintain some fairly sustainable fuel harvesting practices, trees can provide cheap and high energy ROI, enough to bootstrap hydro and wind from which hydrogen can be made and any manner of modern energy (although nuclear and solar and batteries are even more efficient). Biomass can serve as a feedstock for chemicals via steam reforming to syngas and then Fischer-Tropsch to anything else, and biomass is abundant enough for that non-energy purpose even with 8 billion people as long as your prime energy comes elsewhere.

Gotta realize that the fossil fuel energy surplus is often highly wasted on authoritarian regimes and such. Industrious nations can & do find other sources of energy, and there are many to choose from (hydro, wind, biomass, geothermal, nuclear fission, tidal, photovoltaic, solar thermal, ocean temperature gradient, even space based solar, nuclear fusion, etc).

Simply wind energy and hydrogen electrolysis would work. Both are relatively simple.

I think we have a kind of fatalism when it comes to energy sources which isn’t helped by the fact that advocates of one energy source often invest a lot of time in downplaying other energy sources, but we actually have a LOT of good, economic-surplus-compatible options to choose from, and fossil fuels are just one.

The real key is knowledge and precision. From that, and nearly any mix of energy sources and raw materials, comes abundance.