Thank you so much for posting this here! That screenshot looks like the static pages tab, which in the Editor it’s not possible to add static pages, only new collection based pages. If they tab over to the Collection tab and select a collection, then they should be able to add new posts to the blog collection.
If you’re having any further trouble, this seems like a sensitive account / technical issue, and we’re here to help. It is likely we’ll need to investigate and discuss your private account details. As @webdev had mentioned, could you please contact our Customer Support Team?
One of our Customer Support Team Specialists will be able to investigate and respond via email! Thank you so much!