Proxmox is nice for beginners. This is a nice tutorial: https://youtube.com/playlist?list=PLT98CRl2KxKHnlbYhtABg6cF50bYa8Ulo
Proxmox has nice UI for managing Linux Containers (LXC). They act like a computer inside a computer with the advantage that you can clone them. So you can basically save and load them whenever you succeed or fail at something. Proxmox also allows you to install Turnkey Linux containers which have the software you want to run preconfigured in them so that’s also good for beginners.
Only downside is that this is not declarative so it won’t be as scalable as docker or nix. It might be more worth it to learn docker from the beginning but that would also be less friendly for a beginner.
I don’t recommend it unless you just want it for storage or whatever else it does out of the box. It’s basically impossible to tinker with it because it has so many layers of abstraction. At least that was my impression when I tried to edit their nginx config. It had like 2000 lines so I just gave up.
If you want a server that runs services that you download from the internet, don’t buy it. Look at it as a box that does the thing that it promises to do, not as a computer. If you want it to do a different thing, buy a different box that does that. Kinda like a TV. It’s technically a computer that runs some kind of linux but to the user it’s a monitor that also shows videos from the internet.
Also it’s perfectly fine to buy a “NAS black box” but maybe not something I’d buy if I wanted to get into selfhosting. I’d buy it if I wanted to have a NAS running at home with the least amount of “self” in “selfhosting” that’s feasable.