Hi @Marvin_Fuchs.
This has been resolved before (duplicate).
Multiple sections
Please have a look at the solution from How to reset the page counter after every section? - #10 by laurmaedje
Only one section - To switch from arabic to roman
You can also use a shorter solution from How can I switch from Roman to Arabic page numbers without breaking the total page count? - #2 by janekfleper
#let arabic-numbering(..n) = context {
numbering("1 / 1", n.at(0), ..counter(page).at(<last-arabic-page>))
}
// content
#set page(numbering: arabic-numbering)
#counter(page).update(1)
#lorem(9999)
#metadata("last-arabic-page") <last-arabic-page>
// appendix
#set page(numbering: "i")
#counter(page).update(1)
#lorem(999)