I probably read this in the 80’s or 90’s.
We’ve mastered space travel and have found artifacts of a long missing race. One style of artifact is functionally identical to Japanese folding fans, but initially no one could figure out their purpose. But there were thousands of them so eventually some made it into the collectors market as [alien] fans.
Eventually they were discovered to be data storage devices, but much like dropping a CD into ancient Rome, we just didn’t have context to realize what they were sooner.
Ringing a bell for anyone? The memory fragments are pulling up the Heechee Saga, but I don’t have those books any longer to confirm or look up the alien’s name.