I'm having the same issue as well. However, I was able to share my quiz results with the image and title on FB without adding the APP ID.
After going through the steps, I noticed the UI was sightly different, perhaps because I have a business manager. Anyway, when I tried to make the app public, there was no toggle under App Review.
When I go to
business.facebook.com/settings/apps I can see the APP ID. I entered it in the plugin sharing->Facebook App ID field. I'm not sure if I notice a difference.
I'd like some clarification too!