Many publications on arxiv (or biorxiv or medrxiv, etc) are early drafts, or otherwise not scientifically rigorous and wouldn’t be published in an actual journal due to failing peer review. Take what you find there with a grain of salt.

Although you should also take any single peer-reviewed article with a grain of salt as well.

arxiv has a narrow scope, there’s also biorxiv.org but both are for preprints which is a little bit different thing