Package is not being installed

Hi uridrupal, I'm going to take a look at that, thanks for reporting the issue.

I've opened a MR adding the packages back to composer.json. I believe, without using the composer merge plugins, all the required packages need to be included in the main composer.json because submodule versions aren't read and used when those submodules are enabled.

The patch won't fix the problem while it's still a patch because patches are applied after the composer.json is read during composer install, so for now I've had to also require the packages directly in my project's composer.json.

Thanks kimberleycgm, I'll look into that! Anyone else can try the patch and comment if it's fixing their issues.
We'll see for the best practises how to handle this.

For whom hasn't composer and use ludwig...
ludwig.json:

{
    "require": {
        "html2text/html2text": {
            "version": "v4.3.1",
            "url": "https://github.com/mtibben/html2text/archive/4.3.1.zip"
        },    
        "getbrevo/brevo-php": {
            "version": "v2.0.4",
            "url": "https://github.com/getbrevo/brevo-php/archive/refs/tags/v2.0.4.zip"
        },
         "nyholm/psr7": {
            "version": "1.8.2",
            "url": "https://github.com/Nyholm/psr7/archive/refs/tags/1.8.2.zip"
        }
    }
}

and add this row to brevo.module

// Ludwig module integration.
if (\Drupal::hasService('ludwig.require_once')) {
  $ludwig_require_once = \Drupal::service('ludwig.require_once');
  $ludwig_require_once->requireOnce('html2text/html2text', 'src/Html2Text.php', dirname(__FILE__));  
}

Thanks for your participation, I reviewed the code and it's right, composer.json has to be in the main module only.
Unfortunately everyone will have to install the dependencies needed for the mailer submodule even if unused.
I also included the Ludwig.json support.