You should be seeing a RoonServer process and a RAATServer process running. If you aren’t then it’s worth checking the /var/log/syslog/ and /var/roon/RoonServer/Logs/RoonServer_log.txt files for errors.
If the processes are running then do you have a firewall setup on your desktop? That could be blocking the remote’s connection to your core. If so then try disabling it and see if your remote can connect.
So we can better assist you, please describe your network configuration/topology, including any networking hardware currently in use, so we can have a clear understanding of how your devices are communicating.
What kind of remote device are you using? Have you tried multiple? Are they all unable to connect?