The issue with authors actually comes up quite often, for instance here:
It’s “in there” somehow but not really properly documented. It’s mentioned in the Site Variables page where it is singular.
You can add an author section to your config.toml:
[author]
name = "Patrick Kollitsch"
homepage = "https://samui-samui.de/"
content = "sitewide/authorfooter/index.md"
[author.photo]
name = "patrick.kollitsch.jpg"
title = "Der Autor in seiner natürlichen Umgebung"
[author.format]
layout = "card"
There is no real ruling of what to add, it will all be available via site.Author.
The following link lists some uses, but most of them via the data folder.