How can I add a dotted line like bibliography between two texts that are left and right aligned?

[Y.D.X]

Hi, welcome to the forum!

Check 1fr (one fraction of the remaining space):

#align(right, box(width: 20em, {
  set par(spacing: 0.65em)

  let rows = (
    ([Secretariaat:], [Sample address]),
    ([Telefoon:], [Sample phone number]),
    ([E-mail:], [Sample e-mail address]),
    ([Website:], [Sample website]),
  )

  for (left, right) in rows {
    left
    [ ]
    box(width: 1fr, stroke: (bottom: (paint: luma(50), dash: "dotted")))
    [ ]
    right
    parbreak()
  }
}))

(By the way, if you know any community platform specific to your language (Dutch, I guess?), I suggest you comment it under Community platforms)