Hello Giogi!
Thank you for your response. The Version 6.0.62 brought the update and I can see the FR here: https://www.nomachine.com/FR12N03284
Now in the client I have the devices listed. When I try to connect them they are showing a loading spinner and later a red exclamation mark.
I gathered the logs and looked through them but can not find whats going on. Maybe I need to unblock certain ports in the firewall?
Additional info:
server is Windows 7 x64 Professional running NoMachine 6.0.62-5
client is Raspberry Pi 3 Debian stretch running NoMachine 6.0.62-10
Regards Sebastian