We can find the trope "lost technolgy" in vrious genres, mostly fantasy snd science-fiction. It descibes technologies, techniques, or knowledge in a broader sense, that was known/used by ancient civilisations/groups, but has over time become "lost". This trope very often implies/shows the "lost technology" to be more advanced than "current" technology.
I have two questions about this trope, one "practical/archeological", one that i think is more in the realm of literature, myths, and legends:
1.) What are good examples of technology that has been losz throughout the ages? As far as i know we stil don't know how the pyramids were built, or how stonehenge was errected. There must be more curious stuff like that.
2.) Do any historic sources speak of technology that is lost to us and is described to be able to rival modern technogy? Are an of those sources consided to be more than myths or legends? (Stuff like "'greek fire" wouldn't cut it, because even if it existed and subsequently was lost, it pales compared to napalm, termite, etc.)
There's a subtlety of language here that needs to be addressed. When we say we don't know how Stonehenge was built, it's not because we can't provide an answer. There plenty of possible answers, we just don't know which is right. It's not a fill-in-the-blank we're staring mindlessly at: it's a multiple choice with five good answers and the only clues to which is correct have been decomposing underground for thousands of years. If I make you a sandwich, you won't know if I spread the mayo with a knife or a spoon, where I got the bread, how I cut the onions, whether I grew the lettuce myself, or even if I hired someone else to make it. You can make some basic guesses, but you won't ever be able to know how I made the sandwich. "He took the ingrwdients and stacked them together" is just as good of a description as "they stacked the stones to make Stonehenge." Of course, ancient stone circles make a lot better fodder for sensational media than ham sandwiches you've probably already eaten.
Besides the exact chemical make-up of certain incendiary weapons or pigments, there's not really any genuine "lost" techs.