And this can be used for underlying functionality also right? I mean not only to use it in Admin area. I just want to have Custom Tables that have relationship many-to-many so I can do inner joins in my queries.
I'm following the same question in a topic from Facebook Group. The answer, in short, is impossible. The relationship only saves the data in the table mb_relationships. It helps you to connect posts, terms, and users while the main purpose of the extension Custom Table is to help you to save custom fields’ values to the custom table instead of the default WordPress meta table.