Do you have a column {first_author}... NO. That is not a standard column.
If you have a custom column, it always has a # eg. {#first_author}
I think you need to use the
https://manual.calibre-ebook.com/template_lang.html to create one that only grabs 1 Author.
BTW there is no guarantee who is first
FWIW when I started, my device only used file names.
So I had 2 top level folders: 1)By Series, 2)by Authors NOT IN A SERIES
FWIW Some series, like your example, do not always have the same set of authors. IMHO is why the first item is SERIES -Series_index-Title (optional Authors as that is the least important to the sort , if at all)
You can't sort 2 ways at the same time