I have seen that many people claim that the existence of Jesus is almost universally agreed upon by scholars. However, skeptics say a few things:
The New Testament is an unreliable biased source.
Claims made by “bible schools” or theology schools lack credibility compared to traditional university or academic works.
Anything written by people like Josephus (which many biblical scholars reference)lack credibility and most likely forgery.
So what are other extra-biblical source to validate the existence of the historical Jesus that people claim are almost universally accepted by scholars?
When dealing with historical claims from antiquity, it is important to have an appropriate level of skepticism. What this means is that doubting specific, seemingly outrageous, claims can be easily defended, but doubting all claims cannot.
The most important extra-biblical source for the historicity of Jesus is indeed Josephus' Antiquities, but it is three passages in context with eachother that provides this evidence, rather than just one.
The first is 18.5.2, where Josephus speaks of the imprisonment and execution of John the Baptist. This passage is generally considered authentic and is highly valuable because it is extra-biblical evidence for a crucial character in the gospel narratives. This doesn't speak to Jesus directly, but it does suggest that the gospels contain some historical information.
The second is 20.9.1, where Josephus speaks of the death of James. The pertinent text is short, so I'll quote it here:
Festus was now dead, and Albinus was but upon the road; so he assembled the sanhedrim of judges, and brought before them the brother of Jesus, who was called Christ, whose name was James, and some others and when he had formed an accusation against them as breakers of the law, he delivered them to be stoned...
Here we get a mention of two gospel characters, Jesus and his brother James. Generally this passage is accepted as authentic, as it is rather unflattering to James (a breaker of the law) and doesn't call Jesus the messiah (Christ), but rather claims he was called Christ by others.
Finally, we get to 18.3.3 and the so-called Testimonium Flavianum. This passage is different from the one above, as Josephus clearly claims Jesus as a messiah:
About this time there lived Jesus, a wise man, if indeed one ought to call him a man. For he was one who performed surprising deeds and was a teacher of such people as accept the truth gladly. He won over many Jews and many of the Greeks. He was the Christ...
Because of the overtly devotional language here, almost all scholars doubt the authenticity of this passage; however, the fact that the passage once again mentions Jesus is important. It means that Josephus likely said something (perhaps negative) about Jesus here originally, and it has been edited over time. The exact wording is less important than the mere mention of Jesus, as we are looking for historical attestations not historical facts.
When you couple the three passages together, it suggests that Jesus was a historical figure that Josephus mentioned as important during the first century CE. It also suggests that the gospel narratives have some historicity in them, as several of their characters are mentioned as well (e.g. John, Pilate, James).
Josephus doesn't prove Jesus was real, because that is an impossible standard. We have to go on balance of probability. Josephus has nothing to gain by mentioning these figures, thus we wonder why he might. The simplest and most logical answer is that they were real and worthy of note. This doesn't mean that the gospels are perfect history to be read uncritically, but it does indicate that they have historical value and shouldn't be automatically dismissed.
Hope my comment won't get removed as it doesn't answer your question but I seriously wonder why biblical sources shouldn't be taken as serious historical data? Imagine saying "we can't know if Buddha existed because all sources are Buddhist...", Same with Mohammed and so many others... Most of the history writings are from religious, so if you dismiss all of it you won't have much historic material! So, why the new testament shouldn't be considered a serious historical proof that Jesus existed?
If Josephus is the source of so much biblical evidence, couldn't it be possible that Josephus wrote most (if not all) of the the New testament? He, after all, does go into very deliberate detail about the Essenes in one of his books (a sect whose behavior sounds awfully similar to christianity) . He was also in a position (as a Jew turned Roman Citizen tasked with writing the history of the Jewish War) to influence beliefs about the Jews and could have had the goal of creating a new syncretic movement that both pagans and Jews could get behind.