Factual error: Druig leads several warriors outside Tenochtitlan as it was sacked by the Spanish conquistadores, and they live peacefully in the nearby forest, for 500 years. The forest is of course the virgin Amazon forest, as captions say. Small problem; Tenochtitlan was in Central Mexico.
Factual error: There is a billboard in London advertising a display of "artifacts" at the Natural History Museum. British English spells it "artefacts" and the Natural History Museum in London only holds exhibits on natural history. A display of artefacts would be at the British Museum, a completely different institution in a different part of London. (00:07:25)
Factual error: The scenes set in Babylon in 575 BCE have the characters speaking Standardized Arabic to one another. At the time in Babylon, however, Aramaic language was actually spoken - Arabic as a language isn't considered by historians to have emerged until the 1st century CE. There's still Aramaic spoken in some regions of Iraq and Turkey, so it's not like the filmmakers have to use Arabic instead.
Factual error: Thena and some Eternals go to the Amazon. The opening scene shows the Amazon River lowlands. In the Amazon they speak Portuguese. But the Eternals speak Spanish to the natives. A part of the Amazon is in Peru where Spanish is spoken, but this is not the area where llamas (shown) typically live. Llamas are highland animals and are in southern Peru, not northern. (01:06:10)
Factual error: It can be argued that the MCU is not quite our world, but certainly mirrors it closely - after all, the movie makes a point to feature real life dates and events such as Hiroshima, showing that even Cap America's actions in Europe didn't alter the outcome of WW2. It's then quite puzzling to see then Sersi gifting the savages in Mesopotamia a golden dagger that reproduces with precision one of the golden daggers in the tombs from Ur; they were Mesopotamian artefacts, sure, but from around 2600 BC and the scene takes place in 5000 BC.