One way to easily detect whether the #show: appendix rule has been applied is to make the appendix function insert metadata into the document, which you can then query . Note that queries should be inside contextual blocks. Finally, you can use conditionals to choose what should be displayed.
Something like this:
#let conf(
title: none,
doc,
) = {
// stuff here
context {
if query(metadata.where(value: "appendix")).len() == 0 {
outline(indent: auto)
}
else {
let appendix-pos = query(metadata.where(value: "appendix")).first().location()
outline(
indent: auto,
target: selector(heading).before(appendix-pos)
)
pagebreak()
outline(
target: heading.where(supplement: [Appendix]),
title: [Appendix]
)
}
}
pagebreak()
doc
}
#let appendix(body) = {
// stuff here
metadata("appendix")
body
}