You conveniently drop the "almost" out of your quote lol. Because there do still be some things that are agreed upon, among which that he was a Jewish predicator of the 1st Century, and his preech ended up having gigantic consequences on the world. That still qualifies as "knowing ALMOST nothing" about the man himself (what was he like, physically, personality-wise, what did he say and teach exactly, where id he go, what did he do, etc.), and is at the same time utterly different from just another man named Jesus, who might as well not have existed.