The OS is what the software (Roon Server) runs on. It contains the kernel, drivers and additional software needed to run and operate the system. Yours seems to be outdated – an update to the current version might get you up and running again. Even if not, there is usually no support for systems running on outdated software/OS.
It’s very unlikely that anyone, be it Roon Labs or QNAP, is testing on/against outdated software/OS.
PS: Also 2 GB RAM seems rather low for a Core with streaming services enabled. See also: Roon Server on NAS
We strongly recommend 4GB of RAM and an SSD for the Roon databases .