But, my understanding of things like the fake news challenge is that their definition of fake news is probrably news that has been shown by experts, scientists, video evidence, scholars, actual investigative journalists, or similar to be demonstrably false.

The alt-right is already aware that scholars, scientists, and generally educated people believe their news sources to be bunk and that has not changed their opinion. So even if facebook or whoever makes perfect software that blocks crazy info wars articles or other news meeting the definition above, conservatives will cry censorship and find another platform because their chosen platform fundamentally disagrees with them on what is true. People don’t use Facebook to be told they are wrong.