[Resolved] I have set the custom meta for stock as copy and manually update one product and the value synced in...

add_action( 'wcml_synchronize_product_component', function ( $product, $translationsIds, $translationsLanguages, $componentName ) {
	// Only run for variations and only for the Stock component.
	if ( ! $product || $product->post_type !== 'product_variation' || $componentName !== 'stock' ) {
		return;
	}
	if ( empty( $translationsIds ) ) {
		return;
	}

	$product_id = (int) $product->ID;
	$wc_product = wc_get_product( $product_id );
	if ( ! $wc_product ) {
		return;
	}

	// Same logic as WCML Stock component: who actually holds the stock?
	$id_managing_stock = $wc_product->get_stock_managed_by_id();
	$translation_ids_for_stock = $translationsIds;

	if ( $id_managing_stock !== $product_id ) {
		// Parent manages stock: sync parent's _stock to parent's translations.
		global $wpml_post_translations;
		if ( ! $wpml_post_translations ) {
			return;
		}
		$translation_ids_for_stock = $wpml_post_translations->get_element_translations( $id_managing_stock, false, false );
		if ( empty( $translation_ids_for_stock ) ) {
			return;
		}
		// $translation_ids_for_stock may be [ lang => id ]; we need a flat list of IDs.
		$translation_ids_for_stock = array_values( array_filter( array_map( 'intval', $translation_ids_for_stock ) ) );
	}

	// Sync _stock from source to its translations.
	$source_stock = get_post_meta( $id_managing_stock, '_stock', true );
	if ( $source_stock !== '' && $source_stock !== null ) {
		foreach ( $translation_ids_for_stock as $tid ) {
			if ( $tid === $id_managing_stock ) {
				continue;
			}
			update_post_meta( $tid, '_stock', $source_stock );
		}
	}

	// Sync _stock_status from this variation to its variation translations.
	$source_status = get_post_meta( $product_id, '_stock_status', true );
	if ( $source_status !== '' && $source_status !== null ) {
		foreach ( $translationsIds as $tid ) {
			if ( (int) $tid === $product_id ) {
				continue;
			}
			update_post_meta( $tid, '_stock_status', $source_status );
		}
	}

	// Clear caches so WooCommerce sees the new values.
	delete_transient( 'wc_low_stock_count' );
	delete_transient( 'wc_outofstock_count' );
	if ( function_exists( 'wcml_product_data_store_cpt' ) ) {
		$wcml_data_store = wcml_product_data_store_cpt();
		if ( $wcml_data_store && method_exists( $wcml_data_store, 'update_lookup_table_data' ) ) {
			foreach ( array_merge( [ $product_id ], $translationsIds ) as $pid ) {
				wp_cache_delete( $pid, 'post_meta' );
				wp_cache_delete( 'product-' . $pid, 'products' );
				$wcml_data_store->update_lookup_table_data( $pid );
			}
		}
	}
}, 11, 4 );