Removed and reinstalled. At first glance, the error is gone, but you have to follow.
Please tell me, we use Rocket caching, do we need to enable the option https://c2n.me/4fD3QIb.png?
And is it correct to choose “Select default itemType for all post or pages” Creative Work Series to display stars in snippets?
1) Yes, it is better
2) To answer your question, yes.
But itemType should reflect the site content. You can try to “cheat” by using a different itemType, just to show stars in search result, but if you are (very) unlucky this can cause a manual penalty by Google.
3) I don’t understand the question