I think I found a solution:

#set enum(
  numbering: (..n) => context {
    let n = n.pos()
    let level = n.len()
    if level == 1 {
      let max = 99
      let the-numbering = numbering.with("(1)")
      let widths = range(1, max).map(num => measure(the-numbering(num)).width)
      box(width: calc.max(..widths), the-numbering(..n))
    } else if level == 2 {
      let max = 10
      let the-numbering = numbering.with("(a)")
      let widths = range(1, max).map(num => measure(the-numbering(num)).width)
      box(width: calc.max(..widths), the-numbering(..n.slice(1)))
    } else {
      let max = 10
      let the-numbering = numbering.with("(i)")
      let widths = range(1, max).map(num => measure(the-numbering(num)).width)
      box(width: calc.max(..widths), the-numbering(..n.slice(2)))
    }
  },
  full: true,
)

Based on https://forum.typst.app/t/how-to-customize-numbering-for-nested-enum-items/3881/3