Disable Gutenberg in Edit Product screen for WooCommerce 3.4.x or older

wc-products-disable-gutenberg.php

<?php
/**
 * Plugin Name: No Gutenberg for old versins of WooCommerce
 * Plugin URI:  https://gist.github.com/claudiosanches/d0231798eb6041e4911b4bca409ec1ac
 * Description: Disable Gutenberg in Edit Product screen for WooCommerce 3.4.x.
 * Author:      Claudio Sanches
 * Author URI:  https://claudiosanches.com
 * Version:     1.0.0
 * License:     GPLv3
 *
 * @package WC_No_Gutenberg
 */

defined( 'ABSPATH' ) || exit;

/**
 * Disable gutenberg for old versions of WooCommerce.
 *
 * @param bool   $is_enabled If editor is enabled.
 * @param string $post_type  Post type.
 * @return bool
 */
function wc_no_gutenberg_for_products( $is_enabled, $post_type ) {
	if ( 'product' === $post_type ) {
		return false;
	}

	return $is_enabled;
}

add_filter( 'use_block_editor_for_post_type', 'wc_no_gutenberg_for_products', 10, 2 );