Depends on your definition of "truly" new since any idea could be argued to be a mix of all past ideas. But I see truly new ideas all the time without going down in the history books because most new ideas are incrementally building on what came before or are extremely niche and only a very few turn out to be a massive turning point which has a broad impact which is also only usually evident in retrospect (e.g. blue LEDs was basically trial and error and almost an approach that was given up on, transistors were believed to be impactful but not a huge revolution for computing like they turned out to be, etc etc).
