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)
Welcome to home labbing… you poor fool!
Honestly figuring out docker is 50% of the journey with the other 50% mostly being networking. For instance if your looking to start your own Jack Sparrow themed streaming service you’d want to grab a domain name, point it at your ip, open up ports 80 and 443 on your router, install a reverse proxy via docker and set up SSL ( hint: Caddy makes this easy ) and point it at your jellyfin docker container and voila, your very own streaming service you can access from anywhere! Notice the complicated part of all this is mostly the networking and docker setups, not so much the OS that your running. ( Note: don’t open ports without knowing the risks )
Debian is a fine OS but most homelab stuff can be done on anything you can install docker on, even on a windows computer! That’s not to say you shouldn’t learn some Linux server stuff but it isn’t wholly necessary. That being said…
My best advice for getting into Linux servers would be to grab an old PC, laptop or even a raspberry pi and install Debian, raspbian or any other distro on it. Figure out how to log in via ssh and get the thing running headless ( no keyboard or monitor ) and just learning to navigate and do things via the terminal. Some of the basics would be learning to use the package manager to install software, mounting the file system remotely and figuring out how to setup static IPs and such. When your ready go ahead and install docker, follow some tutorials, learn some yaml and your off to the races!