OK, we as we can see, WooCommerce widgets don’t take into account our SKU database query. To fix this you will need to edit a few files:

1. First one – wp-content/plugins/woocommerce/includes/widgets/class-wc-widget-price-filter.php

change this code

if ( $search = WC_Query::get_main_search_query_sql() ) {
	$sql .= ' AND ' . $search;
}

to this one

if ( $search = WC_Query::get_main_search_query_sql() ) {

	$search_ids = array();

	// search for variations with a matching sku and return the parent.
	$sku_to_parent_id = $wpdb->get_col( $wpdb->prepare( "SELECT p.post_parent as post_id FROM {$wpdb->posts} as p join {$wpdb->postmeta} pm on p.ID = pm.post_id and pm.meta_key='_sku' and pm.meta_value LIKE '%%%s%%' where p.post_parent <> 0 group by p.post_parent", wc_clean( $_GET['s'] ) ) );

	//Search for a regular product that matches the sku.
	$sku_to_id = $wpdb->get_col( $wpdb->prepare( "SELECT post_id FROM {$wpdb->postmeta} WHERE meta_key='_sku' AND meta_value LIKE '%%%s%%';", wc_clean( $_GET['s'] ) ) );

	$search_ids = array_merge( $search_ids, $sku_to_id, $sku_to_parent_id );

	$search_ids = array_filter( array_map( 'absint', $search_ids ) );

	$sql .= " AND " . $search;

	if ( sizeof( $search_ids ) > 0 ) {
		$sql = str_replace( '))', ") OR ({$wpdb->posts}.ID IN (" . implode( ',', $search_ids ) . ")))", $sql );
	}
	
}

2. In this file woodmart/inc/widgets/class-widget-layered-nav.php

replace this

if ( $search = WC_Query::get_main_search_query_sql() ) {
	$query['where'] .= ' AND ' . $search;
}

with this part

if ( $search = WC_Query::get_main_search_query_sql() ) {
    
    $search_ids = array();
    
    // search for variations with a matching sku and return the parent.
    $sku_to_parent_id = $wpdb->get_col( $wpdb->prepare( "SELECT p.post_parent as post_id FROM {$wpdb->posts} as p join {$wpdb->postmeta} pm on p.ID = pm.post_id and pm.meta_key='_sku' and pm.meta_value LIKE '%%%s%%' where p.post_parent <> 0 group by p.post_parent", wc_clean( $_GET['s'] ) ) );
    
    //Search for a regular product that matches the sku.
    $sku_to_id = $wpdb->get_col( $wpdb->prepare( "SELECT post_id FROM {$wpdb->postmeta} WHERE meta_key='_sku' AND meta_value LIKE '%%%s%%';", wc_clean( $_GET['s'] ) ) );
    
    $search_ids = array_merge( $search_ids, $sku_to_id, $sku_to_parent_id );
    
    $search_ids = array_filter( array_map( 'absint', $search_ids ) );
    
    $query['where'] .= ' AND ' . $search;
    
    if ( sizeof( $search_ids ) > 0 ) {
        $query['where'] = str_replace( '))', ") OR ({$wpdb->posts}.ID IN (" . implode( ',', $search_ids ) . ")))", $query['where'] );
    }
    
}

Kind Regards