""Folk music is the product of a musical tradition that has been evolved through the process of oral transmission."
It might have been a handy definition up until 1860 when the human voice was first recorded. Today, as a definition, it is simply pretentious.
It seems to me to be a genre that has multiple definitions that cause endless argument.
An example "music that originates in traditional popular culture or that is written in such a style. Folk music is typically of unknown authorship and is transmitted orally from generation to generation."

The first sentence I have no problem with, it happily includes
songwriters such as Ralph Mctell, Eric Bogle, Ewan McColl.
The second sentence is arrant nonsense and even if aurally is substituted for orally it is too narrow a definition in my opinion.