it largely depends on the metal but the issue is with quality, not amount. plus, you don't have much in the way of just iron items these days - you have steel which requires temps quite a fair bit above what's possible in a charcoal/coal-based forge to work. early copper metallurgy utilized ores that were 10%+ metals - much softer, more malleable. these days we work with less than a single percent (but from much larger veins). much smarter people have written about this than me: https://ui.adsabs.harvard.edu/abs/2025GsGe....400323M/abstra...

a better focus would probably be on the fact that there's no longer really easily accessible coal anymore, much less oil. there also are far less trees by which you can make charcoal and firewood (except in certain areas) and that's actually fairly important when it comes to crafting and technology: https://www.postcarbon.org/can-civilization-survive-these-st...