I appreciate I may be pushing the boundaries here of what Meta Box is intended to do.
I would like to enable user specific category selection via a frontend form. The goal here is to enable users to be able to create and assign their own categories to posts, where these categories are not available to other users.
Getting the frontend form is simple enough using the awesome MB Frontend Submission extension.
However, the part I am stuck on is how get user specific categories.
It does not matter how this categories are created or stored. They do not need to be WordPress taxonomy.
I have experimented with MB User Meta, categories on the User page, and also Key Value fields. But so far I have not figured out if this is possible using Meta Box, without significant WP custom coding.
Meta Box does not support creating a user specific category like that. You can create a custom code to do that. After creating a post and a category selected, update the term meta with that user ID. Then exclude this category from the next form by using setting query_args of the field taxonomy. https://docs.metabox.io/fields/taxonomy/