I have again the same problem. I try to put a field with MB view but there is no field. I have the same configuration at a different site and everything goes well. It's a setting page and custom field with a single image. I put all the details at the screens.
Can you please share the whole screen image after deactivating all plugins except Meta Box and MB Extensions? You can find the setting fields under the tab Site. Screenshot https://share.getcloudapp.com/2NulB8Pk