Preview and content moderation widget broken for unsaved entities

The test and the change look good.

Looking at a fuller context of the change...

    // If the entity is not new, grab the most recent revision and
    // load it. The moderation state of the saved revision will be used
    // to display the current state as well determine the the appropriate
    // transitions.
    if (!$entity->isNew()) {
      /** @var \Drupal\Core\Entity\ContentEntityInterface $original_entity */
      $original_entity = $this->entityTypeManager->getStorage($entity->getEntityTypeId())->loadRevision($entity->getLoadedRevisionId());
      if (!$entity->isDefaultTranslation() && $original_entity->hasTranslation($entity->language()->getId())) {
        $original_entity = $original_entity->getTranslation($entity->language()->getId());
      }
    }
    else {
      $original_entity->set('moderation_state', $default->id());
    }

We need to either extend the comment above, Or (probably better) - add a comment above the else {.

This is ready to go

Committed 884786d and pushed to 8.8.x. Thanks!

Will backport to 8.7.x if the tests are green.

I think the backport should happen here https://www.drupal.org/project/drupal/issues/3065804

Thanks @chr.fritsch