How do let all headings what level >2 don't be outlined

[Andrew]

Same concept as in How to create a show rule for table cells other than the first row? - #2 by Andrew and How to avoid ghost numbering in headers? - #5 by Andrew :

#let annex-template(doc) = {
  set heading(numbering: "1.")
  show heading: set heading(outlined: false)
  show heading.where(level: 1, outlined: true): set heading(outlined: true)
  doc
}

#show: annex-template

#outline()

= A

#heading(outlined: false, level: 2)[B]

== C

=== 3rd level