Filter export data using custom taxonomy - Product import export plugin for WooCommerce by WebToffee (https://www.webtoffee.com/product/product-import-export-woocommerce/)

functions.php

<?php // Please do not copy this line
// generalize filter by custom taxonomy
$GLOBALS['wt_custom_taxonomy_name'] = 'product_brand';
add_filter('wt_iew_exporter_alter_filter_fields',  'wt_add_additional_exporter_alter_filter_fields', 10, 3);
if(!function_exists('wt_add_additional_exporter_alter_filter_fields')){
    function wt_add_additional_exporter_alter_filter_fields($fields, $base, $filter_form_data){
        if ('product' != $base) {
            return $fields;
        }
        
        $fields[$GLOBALS['wt_custom_taxonomy_name']] = array(
            'label' => __('Product '. ucwords(str_replace('_', ' ', $GLOBALS['wt_custom_taxonomy_name'])), 'wt-import-export-for-woo'),
            'placeholder' => __('All '.ucwords(str_replace('_', ' ', $GLOBALS['wt_custom_taxonomy_name'])), 'wt-import-export-for-woo'),
            'field_name' => $GLOBALS['wt_custom_taxonomy_name'],
            'sele_vals' => get_custom_taxonomy(),
            'help_text' => __('Filter products by their '.ucwords(str_replace('_', ' ', $GLOBALS['wt_custom_taxonomy_name'])).'. You can export multiple together.', 'wt-import-export-for-woo'),
            'type' => 'multi_select',
            'css_class' => 'wc-enhanced-select',
            'validation_rule' => array('type'=>'text_arr')
        );
        
        return $fields;
        
    }

}
if(!function_exists('get_custom_taxonomy')){
    function get_custom_taxonomy(){
        $out = array();
        $product_categories = get_terms(array(
            'taxonomy' => $GLOBALS['wt_custom_taxonomy_name'],
            'hide_empty' => false,
            ) );    
        if (!is_wp_error($product_categories)) {
            $version = get_bloginfo('version');
            foreach ($product_categories as $category) {
                $out[$category->slug] = (( $version < '4.8') ? $category->name : get_term_parents_list($category->term_id, $GLOBALS['wt_custom_taxonomy_name'], array('separator' => ' -> ')));
            }
        }
        return $out;
    }
}


add_filter('woocommerce_csv_product_export_args','wt_woocommerce_csv_product_export_args');
if(!function_exists('wt_woocommerce_csv_product_export_args')){
    function wt_woocommerce_csv_product_export_args($args){   
        $form_data=(isset($_POST['form_data']) ? Wt_Import_Export_For_Woo_Common_Helper::process_formdata(maybe_unserialize(($_POST['form_data']))) : array());    
        $prod_brand = !empty($form_data['filter_form_data']['wt_iew_'.$GLOBALS['wt_custom_taxonomy_name']]) ? $form_data['filter_form_data']['wt_iew_'.$GLOBALS['wt_custom_taxonomy_name']] : array();         
        if(!empty($prod_brand)){
            $args['filter_by_custom_taxonomy'] = $prod_brand;
        }    
        return $args;    
    }
}

if(!function_exists('wt_handle_custom_query_var')){
    function wt_handle_custom_query_var( $query, $query_vars ) {
        
            if ( ! empty( $query_vars['filter_by_custom_taxonomy'] ) ) {                
                    $query['tax_query'][] = array(
                            'taxonomy' => $GLOBALS['wt_custom_taxonomy_name'],
                            'field'    => 'slug',
                            'terms'    => $query_vars['filter_by_custom_taxonomy'],
                    );
            }

            return $query;
    }
}
add_filter( 'woocommerce_product_data_store_cpt_get_products_query', 'wt_handle_custom_query_var', 10, 2 );