add_action( 'init', 'kruch_custom_taxonomies' );
/**
 * Register custom taxonomies
 */
function kruch_custom_taxonomies() {
    register_taxonomy('userdatatype',
        [ 'userdata' ], [
            'public'            => false,
            'show_ui'           => true,
            'show_in_menu'      => true,
            'hierarchical'      => false,
            'rewrite'           => true,
            'capabilities'      => [],
            'meta_box_cb'       => null,
            'show_admin_column' => false,
            'show_in_rest'      => null,
            'rest_base'         => null,
    ] );
}