Number Special Sections
Sections that are assigned a built-in special style aren’t numbered by default.
To number regular sections as well as special sections, set sectnums and assign it a value of all.
= Title
:sectnums: all
The assignment of appendix numbers isn’t affected by sectnums as their section title prefixes are controlled by the attribute appendix-caption.
Book parts aren’t numbered by sectnums either, instead, they’re controlled by partnums.