Two columns is good, albeit annoying on mobile. But the font. The typeface kills me, and almost every LaTeX-generated document sports it.
:root, [data-theme=light] {
/* --text-font-family: "freight-sans-pro";
}
> "Computer Modern" is used for body text to give it a professional/academic look
arXiv accepts various flavors of TeX, or PDFs not produced by TeX [0], and automatically produces PDFs and HTML where possible (e.g. if TeX is submitted). In the case of the example paper under discussion, the authors submitted TeX with PDF figures [1], and the PDF version of the paper was produced by arXiv. The formatting was mainly set by using REVTeX, which is a set of macros for LaTeX intended for American Physical Society journals.
[0] https://info.arxiv.org/help/submit/index.html#formats-for-te... [1] https://arxiv.org/format/2312.12451
Some fields may use Word files, but in most of physics you would get laughed at...
It is true that most journals will typically reformat your .tex in a different way than is displayed on the arXiv.
In the arxiv you use latex and do everything yourself. There is no editor.