Add taxonomies to Content Blocks (Custom Post Widgets)

function.php

//
// Add Category support to the Custom Post Widget - https://wordpress.org/plugins/custom-post-widget/
// NB - Must set the priority to a high number
//
add_action( 'init', 'add_content_block_taxonomies', 99 );
function add_content_block_taxonomies() {
	register_taxonomy_for_object_type( 'category', 'content_block' );
}