User files (attachments) are stored separately from the database, in file storage. By default, the server file system is used as the file storage.
You can connect S3-compatible file storage in order to store user files in it. To do this, create a bucket and, in the file htdocs/settings_server.php, specify the parameters for connecting to the S3 storage:
define('FILE_STORAGE_TYPE', 'STORAGE_S3');
define('FILE_STORAGE_ENDPOINT', 'http://');
define('FILE_STORAGE_BUCKET', 'bucket');
define('FILE_STORAGE_LOGIN', '...');
define('FILE_STORAGE_PASSWORD', '...');
putenv('AWS_SUPPRESS_PHP_DEPRECATION_WARNING=true');