I picked Nature because it's the best known academic Journal. I'm aware it's not a mathematical journal. I don't think that undermines my point since mathematical journals obviously exist although they lack name recognition with a general audience.

I am pretty sure that journal publication is the norm. I do know mathematics although I am not one myself. The mathematicans I know want/need journal publications as unpublished research isn't counted in their research output. I know Arxiv is typically used for preprints while awaiting review but publication is always the aim.

Don't take it from me though. zbMath did a study finding 60-70 percent of arxiv papers on math end up in peer reviewed journals. https://ems.press/content/serial-article-files/47210.