The first industrial revolution (which btw happened long after the dark ages and well into the early modern era) was marked by a transition to waterpower & stea

The first industrial revolution (which btw happened long after the dark ages and well into the early modern era) was marked by a transition to waterpower & steam (which can also be generated by burning wood) and of course windmills are even older, so it's possible to have happened without fossil fuels - it would just develop differently. Maybe we'd have massive build out of hydroelectric dams, wind turbines, steam engines powered by wood harvested from artificial forests optimized for fast growth/hot burning trees. You could still have air travel by airships & trains will still be workable albeit slower than our trains. Maybe Iceland would be contentious territory due to geothermal resources, like the middle eastern petrostates in the 20th/21st centuries.