The Google Script will check the privacy status of each of your YouTube playlists and set the visibility status of the ones that are either public or unlisted to private. Good option if you would not like the Internet to know about the various playlists you have saved in your YouTube channel.

You’ll have to enable the YouTube Data API available under Advanced Google Services inside the Google Apps Script Editor.

function makeYouTubePrivate() {
  var nextToken = '';

  while (nextToken != null) {
    var res = YouTube.Playlists.list('snippet,status', {
      maxResults: 50,
      mine: true,
      pageToken: nextToken,
    });

    for (var i = 0; i < res.items.length; i++) {
      var item = res.items[i];

      if (item.status.privacyStatus != 'private') {
        Logger.log('Updating ' + item.snippet.title + ', ' + item.status.privacyStatus);
        item.status.privacyStatus = 'private';
        var updateRes = YouTube.Playlists.update(item, 'snippet, status');
        Logger.log(updateRes.status.privacyStatus);
      }
    }

    nextToken = res.nextPageToken;
  }
}