Yeah, the whole Flat Earth stuff is a relative modern re-occurrence.

We've had concrete evidence of a globe Earth and a pretty accurate measurement of the circumference since the 3rd century BC (Erastothenes). ¹
Heliocentrism was theorized by the Ancient Greeks, but we've only had concrete evidence/math since the 16th century (Copernicus). ²

Then in the 19th century, you had the writer Washington Irving who wrote a romanticized biography of Columbus and claimed that folks in the Middle Ages believed the Earth to be flat, which was just not true. ³

And then there was Samuel Rowbotham, another writer who just made up a whole load of bullshit and kind of brought the conspiracy theories underway. ⁴

¹: https://en.wikipedia.org/wiki/Flat_Earth
²: https://en.wikipedia.org/wiki/Heliocentrism
³: https://en.wikipedia.org/wiki/Myth_of_the_flat_Earth#Irving's_biography_of_Columbus
⁴: https://en.wikipedia.org/wiki/Samuel_Rowbotham