Thank you for the details!  This helps finding a good place to document this.
A link to function parameters from the top of the section may be good.
But maybe we need a sidebar link on all pages that goes to a description of doc conventions! (and includes link to basic syntax doc, function parameter glossary, tutorial).

(As you thought, there are notations in the docs (and even in some docstrings) that are documentation conventions but not valid Python, such as "range(start, stop[, step]) -> range object")

Even the enty for '* (asterisk)' in the general index https://docs.python.org/3/genindex-Symbols.html links to places explaining *args, not * alone.

I agree that the glossary entry for parameter is the best place to link to: it’s short and complete and can link to language reference for more.