Playing around with forms and ajax but ran into problems. When I add a form element before the ones that should be added dynamically it's stops working if the element is required. I thought I could solve it by skipping required and validate instead but it gave the same result (and I do like to have the red star :-).
I'm to much of a rookie in Drupal 8/9 to have any clue on how to solve this so I really hope there is someone with a solution.