Creating a custom module caused "The website encountered an unexpected error. Please try again later."

Drupal 9.2.7 on XAMPP 7.3.29 , 7.4.21 on Windows 10 Home.

I tried to create a custom module which allows global JavaScript and CSS (effective in all webpages in my website), by creating the directory root/modules/globalrs with the following files:

globalrs.info.yml

name: globalrs
type: module
core_version_requirement: ^8 || ^9
description: 'globalrs'
libraries:
  - globalrs/globalrs

globalrs.module

function globalrs_preprocess_page(&$variables) {
  $variables['#attached']['library'][] = 'globalrs/globalrs';
}

globalrs.libraries.yml

globalrs:
  js:
    behavior.js: {}
  css:
    theme:
      style.css: {}

style.css

* {
    background: red;
}

My problem

My problem is that the website won't load, instead the following error appears:

The website encountered an unexpected error. Please try again later.

Even if I delete the module directory and flush all caches (flushing all cache_ tables as well as the cachetags table, and flushing the browser's cache, the website still has that error;
Since that error is generic, I don't know how to start to solve the problem.

A bug as a possible reason

It may be that the problem started after I have added $settings['rebuild_access'] = TRUE; to the end of /sites/default/settings.php, saved the file and then navigated in my web browser to localhost/example.com/core/rebuild.php, where I got the following error:

Fatal error: Uncaught PDOException: SQLSTATE[HY000] [1044] Access denied for user 'example.com'@'localhost' to database 'example.com' in

Edit (removing the rest of the error messages because this is caused by an unrelated error while restoring a backup):

I believe that the problem happened sometime when I tried to restore a backup of the website to a new empty database with the same name which was registered as associated with the database user (or appeared to be such) but actually wasn't

Update - solution

I paste this here after Clive deleted my answer:

I revoked all database-specific privileges that the database user had on the database with the same name and then re-granted these database-specific privileges¹ to that user; I could then access the website.

Before you create a custom module set

• All messages, with backtrace information

in admin/config/development/logging. This option is available in Drupal core without any dev tools installed.

Then you get a more helpful error message if anything goes wrong.

With default

• None

the error message gets replaced by "The website encountered an unexpected error. Please try again later.". The only purpose of this message is to hide the real error in production environments.

If it's too late and you can't open the admin UI anymore you can still enable all error messages in settings.php:

$config['system.logging']['error_level'] = 'verbose';

Don't remove the module code, this makes things worse. If you can't go forward or backwards, you can't fix the error with the more helpful error message and you can't uninstall the module because it is broken, then rollback the entire site from a backup or snapshot you've made before you've created the module.