Operation Avalanche is a conspiracy thriller film released in 2016. It is of a deconstructive parody genre that assumes as if the Apollo moon landings did not occur and gives a fictional backstory on how secret agents managed to “fake” the moon landings.
Flat-Earthers took footage from the movie, then modified them to make them more convincing, and presented the result as if it is a recently discovered video on how the moon landings were “faked.” The video then spread in flat-Earth communities as a hoax.