There is decent circumstantial evidence that Mark was Peter's companion and his gospel was based on Peter's teachings and testimony.
Luke was a companion of Paul. Luke openly states in the introduction to his Gospel that he talked to and investigated the eyewitnesses.
There is absolutely no propaganda value for the church to name two canonical gospels after obscure low-ranking Christians like Mark and Luke. That's a line of evidence for the authenticity of the authorship.
The is circumstantial evidence that Matthew's gospel is based on a Hebrew manuscript Matthew wrote and was later compiled and edited into a Greek edition.
John is the only one where I think authorship is truly questionable.
Early church bishops in the late first century and early second century were quoting from these gospels, so we know the gospels are first century transcriptions written when the eyewitnesses or people who knew the eyewitnesses were still alive.
You can say everyone is lying, but then you are getting into conspiracy theory land, and you would also have to explain why Peter, James, and Paul were willing to be executed for something they knew was a lie.