code>$this->prepareInvokeAll($entity, 'entity_prepare_form', $form_state); in EntityInlineForm::entityForm call is inconsistent: $entity is the child entity but $form_state->getFormObject() is the parent form object. The hook documentation says "Acts on an entity object about to be shown on an entity form" but the form state does not belong to this entity.
This easily leads to fatal errors as a node form will get a paragraph set on it. I strongly suspect https://www.drupal.org/project/inline_entity_form/issues/3396757 🐛 Inline editing is broken on content that have workflows enabled Needs work is due to this, for example.
None required. This is simply so.
I don't have the slightest idea. But I will work on this the next few hours.
Closed: outdated
2.0
Code
@charlie: 2.x branch is revoked. A thorough implementation is done in the related issue.