Vim's built-in manual is the authoritative source of information and documentation on every Vim feature, including configurations, built-in functions, and even Vimscript. While not the most beginner-friendly interface, if you know how to look through it, you can find what you need.
Start searching by executing
:help [subject], or
|Configuration, function name, or any other keyword with significance to Vim. Keywords with a leading colon |