Module development and code questions

I am playing with code to define base fields in a custom entity created in a module.  For example...

Hi friends,

I have multilingual site. And there are content originally created in 'es' (Spanish) language. Now, we have to change all those existing content to 'en'. In my custom drush command, tried below thing but now working --

After loading the node object trying to change it like this --

$node->set('langcode', 'en');
$node->save();

It is giving this error --

Hello Drupal Commerce community,

I am developing a multi-vendor marketplace for a client in Iran and Afghanistan, where the official calendar is Jalali (Solar Hijri / Shamsi). I am using Drupal Commerce with the Commerce Marketplace module as the foundation.

Hi everyone,

I am developing a custom Drupal module and I need to pass data dynamically from one module to another. For example, Module A generates some user-related data, and Module B needs to use it for custom processing.

Here’s a simplified scenario:

// Module A
function module_a_generate_data($uid) {
$user = \Drupal\user\Entity\User::load($uid);
return [
'username' => $user->getAccountName(),
'roles' => $user->getRoles(),
];
}

I am trying to create content by a script running outside Drupal. I know this is possible, and probably done better, using REST. But the script below is so simple to set up and works very fast that I'd like to try and get it to work in D10->, like it did in D7.  

This code (from the final entry in this post), works to retrieve user and node data, running, for testing purposes, inside the Drupal root folder...