The appeal to ancient wisdom is a fallacy where someone assumes that concepts and knowledge from ancient times are superior to modern ones. In reality, just because they are from ancient times, it does not mean they are better than modern ones. On the contrary, in practically all the cases, we know a lot more than our predecessors.
Flat-Earthers often show us that in the past, people from various cultures believed that Earth is flat. Using it as “evidence” of a flat Earth is the fallacy of appeal to ancient wisdom.