The exact term may not have existed in Ancient Rome or the Middle Ages but the concept was there.
This is a lefty article so you can disregard the propaganda but some of the history is interesting:
https://today.usc.edu/conspiracy-theories-past-present-qanon-usc-experts/
Your article mentions social media which is a huge factor in promoting a lot of the stupid (IMHO) conspiracy theories such as the Twin Towers being demolished by the USA, no moon landings, no nuclear weapons ever developed, etc.
Although in the case of my daughter it is also based a lot on distrust of the government regarding the Covid response. While that distrust is justified and prudent, the social media folks use that in order to say that EVERYTHING the government says is a lie.
And then folks just go with it rather than thinking for themselves. (Like doing a quick search on “when was the first time conspiracy theory was used”.) Unless of course the CIA planted that link to a fake article they dated 1863 to throw us off the track!
My daughter listens to Candace Owens. Candace started off okay - now she’s a bit out there with some of her stuff.