THEME.theme

/**
 * Implements hook_preprocess_HOOK().
 */
function THEME_preprocess_paragraph__button_icon(&$variables) {
  $paragraph = $variables['elements']['#paragraph'];
  $icon = $paragraph->get('field_icon_button')->getValue();

  if (!empty($icon)) {
    $entity = \Drupal::entityTypeManager()->getStorage("media")->load($icon[0]['target_id']);
    $variables['button_icon'] = $entity->field_media_svg->entity->getFileUri();
  }
}