Programmatically update products

I am building a site with Drupal 9 and Drupal Commerce 2 (Drupal Commerce Kickstart).

The site is complete and I have already entered all the products via Feed (there are over a million). Now I'm looking for a way to periodically update the products automatically (prices, availability, etc.)

In an old site that I had made and which was developed with Drupal 7 and did not use Drupal Commerce, it was very easy to update the nodes (products) through some scripts I had made, while in this case it is not that simple.

I thought about updating with Feed, but it's really too slow, in fact I can't update more than 20/30 products in each cron cycle; I therefore need to use a customized and faster solution. The first feed upload also took a long time.

I tried to create a php script that calls the entity of the nodes I want to modify like I did with the old site, but I can't figure out how to do it. I tried to follow this guide for Drupal 8, but I'm probably wrong to use some function or something is changed for Drupal 9.

Can someone help me?

Using cron to execute feeds is pretty slow, so what about executing feeds with drush?

Here is a simple drush script I use to import feeds.

Execute it like this:

drush php-script import_feeds.php

Note that you need to use the Drupal id of each feed to import by ID.

import_feeds.php

<?php

/**
 * @file
 * Import feeds.
 */

import_everything_in_order();
    
/**
 * Import all feeds in order of dependencies.
 */
function import_everything_in_order(): void {
  $id_user = 1;
  $id_media_image = 7;
  $id_page = 3;

  $feeds_to_import = [
    $id_user,
    $id_media_image,
    $id_page,
  ];
  foreach ($feeds_to_import as $feed_to_import) {
    unlock_and_import($feed_to_import);
  }
}

/**
 * Unlock a feed and then import it.
 *
 * This ensures that dependency import doesn't fail
 * due to locked feeds.
 */
function unlock_and_import(int $feed_id): void {
  exec("drush feeds:unlock $feed_id -y");
  exec("drush feeds:import $feed_id -y");
}