True nas is nas software that moonlights as a server. Debian is a linux distro commonly used as the operating system for servers due to its incredible stability and reliability among other things. So reliable infact that it’s used as the operating system for true nas scale! So unless your using the core version (that runs bsd) then your already using it. As far as rawdogging Debian on your hardware goes, id recommend against it unless you’re looking to seriously up your admin game. No web interfaces, lots of time in the terminal ( command line ) and more configuration files than is anyway reasonable. And we haven’t even started on virtual machines like proxmox ( also Debian based! ) or container critters like docker and kubernetes. (Iirc true nas uses kubernetes under the hood)