Being entirely naive to squid prehistory, the wikipedia page for squid shows two apparent-to-me squid fossils [0]. Is there some nuance here that I'm not aware of?
Not sure about squids in particular, but the easiest way isn't necessarily to find remains, but to see negative prints on sediments.
Tons of fossils are "negative prints on sediments". GP's assertion that "If humans didn't exist while they do, we would have never known about them" is clearly wrong.