I couldn't find the passage, but Edward Gibbon's Decline and Fall of the Roman Empire had a quote along the lines of, "there were so many relics of the holy cross claimed in churches across Europe that one could assemble them into a small forest".
Historians who specialize in that time and area are (for obvious reasons) amongst the most frequently religious academics outside of actual theologians, so most of them have enormous confirmation biases as well.
This is known as “mythicism.” The problem is that it basically requires you to believe in a vast conspiracy by historians and/or that nothing from history can be verified via textual sources. The basic argument against it is that it makes any sort of critical analysis of the past nearly impossible.
It's not exactly tinfoil hattery not to automatically trust the objectivity of people whose deeply held but completely unscientific beliefs rely on a specific conclusion.
Especially not when those beliefs are inherently authoritarian and have been the enforced default for billions of people for over a millennium.
It's not a conspiracy because no one says they planned to do it. It's just being skeptical. If they want to believe something then they're more likely to think evidence confirms that belief. Also, since that was the default view, they're more likely to accept it. Assuming that they must be right is not the only way we can trust historians. I'd argue the only way to really trust them is to assume they can be wrong and analyze what they say and what they're basing it on.
The thing about that is we know the people you're saying that would need to conspire and lie absolutely did because literally everything in their gospels is made up - beside those all you have is few later people vaguely saying Christians exist which no one doubts
Then if he did exist and was in anyway significant we have to ask why did none of the contemporaries write about him or events when we have plenty of writing about less important things from the exact time and region.
There's only one thing I need to have that proves those crosses are the one real cross. The infallible St. George Michael said it best: "Yes I gotta have faith. Ooh, I gotta have faith. Because I gotta have faith, faith, faith. I gotta have faith, faith, faith."
One can read Josephus and Jewish literature that says he wasn't the Messiah. The historical record is there.
Was he the Messiah? That's where the evidence is lacking.
I'll take another moment to again promote, The Passover Plot. It's a remarkably good scholarly historical look at the life of the man as best we can understand it. I came away respecting Jesus as a very clever religious guy who deftly engineered himself to be on that cross because he was fucking brilliant and he believed he was the one. Great read!
The only religious artifact that I am genuinely curious about is the shroud of Turin even if it's not from that time the imprint thing is still like wtf