Countless is my guess.

How did the Polynesians find Tahiti? What did Aristotle write about in his lost book on economics? How did the Romans mix holographic glass at nano scales? How was the Amazon cultivated to have mostly edible plants? What was lost in the wake of every culture pillaged by the Mongols?

We’re advanced today because oil has given us the energy to build stuff. But we only know a sliver of the amazing things that have ever been learned.