With “apt-config dump”, one can see lots of options, but they mostly are not documented, so for example APT::Cmd::Pattern-Only (which only shows up in Binary::apt:: so even “apt-config dump” hides some options unless they are used anywhere). I would expect apt.conf(5) to document any and all configuration items one can do to apt*, either directly or by other manpages referenced from “SEE ALSO”.