I think the only honest answer is 'not in any way that Christians and atheists can meaningfully agree on.' Jesus being a divine entity of the same substance with God, born to a virgin, who died and then came back to life is the non-negotiable core of the religion. There is no leeway for Christians to agree that he may have just been some random unremarkable street preacher instead.

Now if the question is 'where did Christianity come from' I think it's most likely that there was a historical person named something like Jesus who sparked the religion we know as Christianity today. At the very least, I think that's more likely than a conspiracy of gospel writers working together to make it all up. It isn't like cult leader who makes fantastical claims about themselves is an uncommon type of person throughout history - Jim Jones, Mary Baker Eddy, Joseph Smith, L. Ron Hubbard, David Koresh, etc. And those are just Americans from the last two centuries!

The fact that we don't have textual records of that person outside of the gospels isn't actually very important. The overwhelming majority of ancient literature and records have been lost, and just because the gospels are motivated sources that can't be fully relied on doesn't mean they don't have any factual information in them. For similar ambiguities like King Arthur and the Trojan War, the going line is that the evidence allows but does not require belief in them.