When activating the Filter by Taxonomy dropdown in a relationship field this dropdown will fill it will ALL term from every Taxonomy registered to that Post Types.
I want to restrict the taxonomies that are being queried.
The “Filter by Taxonomy” isn’t the correct working, because this is a “Filter by Term” and not Taxonomy.
Screenshot of incorrect label: https://drive.google.com/file/d/1CdDfanyoj3cww57VAat2clYEuwUTDPHI/view?usp=sharing
The reason why we want to filter the Taxonomies, is because plugins like Yoast SEO and SearchWP use Taxonomies under water with really really really large amount of terms which produce Slow Queries.
I have checked the code and there is no filter available on
// get connected taxonomies
$post_taxonomies = get_object_taxonomies( $post_type );
Related issue https://support.advancedcustomfields.com/forums/topic/custom-taxonomy-filter-for-relationship-field-backend/