An example off the top of my head, I remember these absolutely flawless granite vases they found in the pyramids. The machining and precision required to make something so simple like those vases is something we cannot replicate even today. I will try yo see if I can dig up some vids and links for you because there is other stuff too. The granite vases and urns kind of stood out for me because they were so innocuous and simple, and yet we are absolutely not able to make them, even today.