So when you feed Roon the IP it searches for a while then says it can’t find it? Are you attempting to connect over a wire or wrelessly? If the latter, I suggest going wired first, then worry about getting it to work wirelessly. Also, if Roon does see the server you’ll have a conflict since you can’t have more than one machine managing your library (unless you have another license).
When I first got Roon Server up and running on my NAS and looked for it on my iPad, I first had to decertify my Roon Core machine, even though it was turned off. When I turned it back on I then had to tell Roon I was now running it as a “remote”. If all you have is your Core and your new NAS server install, I’m not sure what the exact scenario would be. You might have to demote your core to a remote before you can see the NAS as a “library”.
I take it you’ve already pointed the Roon server on your NAS to where your music files are. This can be tricky as there is no way to browse for them (yet?) and it’s not obvious what the paths are. On mine, the network paths are various subdirectories of \[server name]\media\music. On the NAS this translates to “volume1/media/music…”. If you don’t have any music mapped to the new server you won’t see it as a library in Roon.