Yoast SEO allows you to set categories as a primary term for posts and pages. In some cases, you might want to allow your users to use additional, custom taxonomies to be used as a primary term.
wpseo_primary_term_taxonomies filter allows you to alter what taxonomies are available to be assigned as a primary term.
The example below shows how you can use the filter to add a taxonomy to the list of potential primary terms.
The example below shows how you can use the filter to remove a particular taxonomy from being selected as a primary term.