License of QT VNC Server Add-on

I was reading up on VNC functionality in QT (Commercial add-on: Qt VNC Server) and was surprised that I couldn’t find the source anywhere and it seems to be only available under the commercial license. As a QT Add-On and released QT Work by the QT company I would think that this should be released under GPLv3+? Is my understanding of the license agreement between the KDE Free Qt Foundation and the QT Company wrong here? Is it somehow not covered because it is in preview?

I would really like to try and play around with this functionality and potentially incorporate it into a private project if I could get access to it freely…