If you have a multi-author site where each author works on a separate topic, you can limit their access to a particular category or media. This helps you run your site efficiently with a good editorial workflow. In this article, I will show you how to restrict authors to a specific post category or media in WordPress.
Limiting Author Access to a Category or Media
1. First you need to install the Restrict Author Posting plugin: https://wordpress.org/plugins/restrict-author-posting/.
2. When this plugin is activated, you should see this section in the edit user menu – “Restrict Categories in which this user can post to”.

3. Select the category of your choice. You can have multiple categories selected at the same time.
4. If you want this author to only use their own uploaded media files you can also enable this option – “Restrict using his/her own file in Media”.
5. Save the updated author/user details. Now when this author creates/edits a post they will only have access to the previously selected categories.

6. WordPress Media Library won’t show any media file that this author didn’t upload.

You can repeat the same process for all of your authors.
That’s it! You have successfully restricted authors of your site to specific categories and media files. If you have any questions feel free to share it in the comments.
ed says
the plugin has been removed due to security issues. please update or delete this post.
https://wordpress.org/plugins/restrict-author-posting/