There is common incorrect usage of the term "conspiracy theory". A conspiracy is a plot among multiple people to commit a crime. Fleeing to Argentina would not have been a crime, thus it could NOT be a conspiracy theory for Hitler to have fled to Argentina. There are people in the majority of legal jurisdictions in the Western World specifically in prison for conspiracies. So conspiracy theorists as police detectives are common. Convictions for people for doing conspiracies are quite common. People  being in prison for conspiracy is common.

So while conspiracies are common, Hitler fleeing to Argentina cannot be one of them, by definition. Also, this specifically quoted text is using "conspiracy theory" to refer to a false theory, a totally rude and pretentious usage of the phase that muddies the English language.

Every bit as valid as an opinion because the issue is NOT settled:
"The idea that Hitler and Eva Braun committed suicide in their bunker in Berlin on April 30, 1945 is a conspiracy theory. Adolf Hitler fled to Argentina in 1945."