I’ve successfully used Peter Wriight’s HOWTO to set up a FreeNAS Roon Server VM and followed the library migration guide at Roon. In setting up the server, I did some things different.
I used the current Debian release
I left networking configuration to DHCP because Debian includes an MDNS responder and configures it during installation. The server instance is known by its hostname in domain local.
I used CIFS for file sharing as my music was in an iTunes media directory elsewhere on the FreeNAS server
I did learn that Roon CIFS is a bit finicky Host names are case sensitive as are share names. I had to poke around in the FreeNAS share configurations to get the proper case.
The VM approach appeared to be pretty lightweight by telling Debian to pass on GUI installation.