On the contrary, ArXiv is for pre-prints, i.e. not (yet) peer-reviewed. Off the top of the my head, it was initially used by physicists who often have huge collaborations and long reviewing time. Then the ML community invaded the space later on. This does not mean a peer-reviewed paper cannot go there of course.

Most of the times the peer review version has a copiright restriction, so the arxiv version is the finañ draft that may have small differences.

As an academic, I always thought of arxiv as where you put your papers first, before they are peer reviewed. Before that we used our webpages, but they kept breaking.