Thank you for your fast reply and even more thank you for your example code!!
It works now! I somehow overlooked that I can use toUtf8() on a QString.
You example put me in the right track and now I can adjust basic window properties with my json file
Now just need to work on auto copy this file into the apps resources at runtime.

Here is my working code::

Qt Code: 
  1. QString settings;
  2. QFile file;
  3. file.setFileName("/tmp/settings.json");
  4. file.open(QIODevice::ReadOnly | QIODevice::Text);
  5. settings = file.readAll();
  6. file.close();
  7.  
  8. QJsonDocument sd = QJsonDocument::fromJson(settings.toUtf8());
  9. qWarning() << sd.isNull(); // <- print false :)
  10. QJsonObject sett2 = sd.object();
  11. qWarning() << sett2.value(QString("title"));  // <- print my title
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Thanks again, totally made my morning

Laszlo