Flysystem for Drupal

cd /path/to/drupal/root
composer require drupal/flysystem
drush en flysystem

$schemes = [
  'local-example' => [ // The name of the stream wrapper.

    'driver' => 'local', // The plugin key.

    'config' => [
      // Cache filesystem metadata. Not necessary for the local driver.
      'cache' => TRUE, 
      ...
      // This will be treated similarly to Drupal's private file system
      'root' => '/path/to/dir/outsite/drupal',
      // Or,
      // In order fo the public setting to work, the path must be relative
      // to the root of the Drupal install.
      'root' => 'sites/default/files/flysystem',
      ...
      'public' => TRUE,
    // Optional settings that apply to all adapters.
      // Defaults to Flysystem: scheme.
      'name' => 'Custom stream wrapper name',
      'description' => 'Custom description',
      // Uploads each file to an extra endpoint tha tis considered "write only"
      // Functions as a backup.
      // Note: only supports one replication endpoint.
      // Note: Use as a replication endpoint does not prevent that endpoint from
      //   also being used for other purposes. 
      'replicate' => 'ftpexample',
      // Serve Javascript or CSS via this stream wrapper. This is useful for
      // adapters that function as CDNs like the S3 adapter.
      //
      // Note:  if you have configured multiple flysystem schemes, you can only
      // configure one scheme to manage CSS and JS files.  If you do happen to
      // configure multiple schemes, the last scheme defined with the following
      // parameters will be the one actually used for storing and serving CSS and
      // JS.  @see https://www.drupal.org/project/flysystem/issues/3056455
      'serve_js' => TRUE, // Serve Javascript or CSS via this stream wrapper.
      'serve_css' => TRUE, // This is useful for adapters that function as
      // CDNs like the S3 adapter.
    ],
  // Used as a replication endpoint for 'local-example' (see the 'replicate'
  // option) but may still be used as a standalone endpoint.
    'ftpexample' => [
      'driver' => 'ftp',
      'config' => [
        'host' => 'ftp.example.com',
        'username' => 'username',
        'password' => 'password',
        // Optional config settings.
        'port' => 21,
        'root' => '/path/to/root',
        'passive' => TRUE,
        'ssl' => FALSE,
        'timeout' => 90,
        'permPrivate' => 0700,
        'permPublic' => 0700,
        'transferMode' => FTP_BINARY,
      ],
    ],
  ],
];

// Don't forget this!
$settings['flysystem'] = $schemes;