* Fixed various more mismatches between frontend and backend input validation:

    - [DH#671] Fixed conditionally making components required/optional via backend logic.
    - Fixed validation of empty/optional select components.
    - [#4096] Fixed validation of hidden (with ``clearOnHide: false``) radio components.
    - [DH#667] Fixed components inside a repeating group causing validation issues when
      they are nested inside a fieldset or columns.

* [#4061] Fixed not all form components being visible in the form builder when other
  components can be selected.
* [#4079] Fixed metadata retrieval for DigiD failing when certificates signed by the G1
  root are used.
* [#4103] Fixed incorrect appointment details being included in the submission PDF.
* [#4099] Fixed a crash in the form designer when editing (user defined) variables and
  the template-based Objects API registration backend is configured.
* Update image processing library with latest security fixes.
* [DH#673] Fixed wrong datatype for field empty value being sent in the Objects API
  registration backend when the field is not visible.
* [DH#673] Fixed fields hidden because the parent fieldset or column is hidden not being
  sent to the Objects API. This is a follow up of #3890.