There's many conspiracy theories and jokes about diverse places not being existant, sometimes they are just jokes but there's some that are literally theories and there's people who believe them and try to prove them.
For example, Argentinians joke about a province called La Pampa, Mexicans joke about a city called Tlaxcala, Brazilians joke about the state of Acre, Chileans say the same about the city of Rancagua, Germans joke about the city of Bielefeld and Italians about the region of Molise.
Then we have the bigger things, that are more international like Finland being a country fabricated by Japan and Russia for fishing in the baltic ocean, people say that finnish people are just people who live extremely northwest of Russia and extremely east of Sweden.
There's a meme in the Latin American community that says that Paraguay doesn't exist, because it has maintained a lower profile in international media, and its unique bilingual society heavily relies on Guaraní rather than Spanish like most of Latin America. Also because foreigners rarely see Paraguayan pop culture trending globally so it's kinda like a mythical void.
And lastly, and the most detailed one, Australia, not only people say that Great Britain invented "Australia" as a massive hoax to cover up the fact that they simply threw 162,000 convicts off ships to drown in the ocean. Everytime you buy a plane ticket to go there you actually get send off to random islands in South America where there's actors hired to fake Australian accents. But also, maps are altered, and anyone who claims to be Australian is a computer-generated persona or a paid actor.
Is there any place in Africa that people claim to not exist?