Not exactly this - it was just an example, but thanks!
Beamer offers a flexible way to display content at the beginning of each part, section, or subsection of your presentation.
It also allows you to fine-tune what appears in the outline.
Combined, these features let you do almost anything: show the overall outline, show only the current section and its subsections, or just the current section and subsection, show the current section and subsection with all the others shaded, etc.
I’m quite sure Typst can reproduce all of these behaviors by programming each case as needed. However, I’m not a programmer, and I was wondering whether there’s a package that already implements these kinds of features - something I might have missed.