Sorry for not answering sooner - got bogged down with work yesterday. I see you already got a response, but thought I'd write up what I had in mind anyways :)

The benefits

I want a computer that just works, to the extent that that’s possible. I’ll fix stuff that needs fixing, but ideally I don’t need to do much.

That's great, and good news, this is very easy to achieve with NixOS.

As the other commenter said, rather than (imperatively) running commands like apt install, you configure the entire system through your "nix config". In the simplest scenario, that's just a single file which gets auto-generated when you install NixOS, and if all you need/want is to add some packages, then that's enough (I'll get to different approaches below). In other words, NixOS is declarative rather than imperative: you use the config file to "declare" what the system should look like, and it's Nix's job to ensure that your system adheres to this.

I need to emphasize though, that this is not just about packages, but about every single piece of configuration you could possibly touch on your system. I am currently managing 30+ NixOS machines from a single centralized config, and I have not once edited or even opened a single config files on any of these machines, ever.

Nix comes with a vast package repository: , but just as importantly, with a vast collection of "modules". Think of modules as an abstraction for all the little things you would need to configure to get something running.

Let's take everyone's nightmare configuration as an example, getting Nvidia GPUs to function properly. This is the ArchWiki article on how to do so, and the Debian Wiki does not make it look any simpler. For NixOS, it should be as simple as adding this to your nix configuration file:

hardware.nvidia.enable = true;
hardware.nvidia.open = true; # use the open source drivers; set to false if you want the proprietary ones
hardware.nvidia.nvidiaSettings = true; # optional - will enable the Nvidia settings menu

Of course, all the same complicated steps as with any other distro are necessary "under the hood", it's just that with NixOS, someone else already has "declared" what the system needs to look like for Nvidia GPUs to work, and abstracted it behind these easy-to-use config options. There's currently more than 20.000 such configs options defined, which sounds intimidating, but you only need to use those you actually want to use. For example, let's say you want to install and configure a jellyfin server.

Again, all that is necessary to be up and running is

services.jellyfin.enable = true;

but if you want to customize the install, you can simply search for all available options. Also note that if you ever disagree with how a package/module is built/installed/configured, you can just overwrite the "official" way, though at least in my experience, that is basically never necessary.

OK, back to you.

Let's say you have successfully configured the system as you want it to be - KDE5 installed, your favorite packages installed, Steam configured with programs.steam.enable = true;. Now the worst case happens, and your SSD hits the shitter; it's dead, completely unrecoverable.

Good news: as long as you have a copy of that configuration.nix file, you can be up and running with the a new harddrive and exactly your same, old system in a matter of minutes.

Another scenario, let's say you manage to brick your install (somehow). No sweat, reboot your PC, the previously used NixOS configuration is available as a grub (or systemd-boot) entry. Does not matter if you ripped out all the drivers, switched from KDE to Gnome in the mean time or anything else.

Essentially, disaster recovery is easy in NixOS, even if it is necessary very, very rarely, because nix will already warn you "yeah this doesn't work" when you are building the system.

The Nix language

You have already seen some of it above. Most people say NixOS is not a beginner distro, and that opinion is mostly due to the Nix language. It's... not pretty, but its learning curve is not bad if you just want to do "basic" stuff like configuring your system in the way shown above. For more advanced topics, there is a steep, but not very long learning curve. If that is worth it is up to you; there is no need for it, but it does allow you to write your own modules, and to leverage a full turing-complete programming language inside your configuration. But IMO, just learn as you go, no need to try and study the language just to use NixOS.

Going wild

For a single machine, the single configuration.nix file is perfectly fine. If yo only have a single machine anyways, I'd say stick with that.

As soon as it's 2 or more machines though, it makes sense to move the configuration elsewhere, in a single project which you can back up (usually, via git). This also allows you to reuse parts of your config - for example, if your user is always the same, and KDE should always be there,.., you can define that once and then import that into the inidividual machine's config. You then simply tell nix "build this config on that machine".

There are a ton of awesome projects in the "nix ecosystem", so to speak, which you can also leverage: for example, you can add home-manager to your config, and then use your existing configuration but extend it with config for inidividual users' environments, like customizing KDE itself, configuring git, ssh, your terminal,... You said you are not a customizer, so this probably does not apply to you that much, but it's still good to know that it is easily possible.

Other projects add capability for secure secrets management, for things like turning Nix into a very good approximation of SteamOS,...

TL;DR:

NixOS makes tedious things simple, and disaster recovery trivial. It offers more (and fresher) packages then even the allmighty AUR, while being stable as a rock.

You will never have to re-solve a problem, no matter how long ago you originally solved it.

Well, NixOS is mostly for enthusiasts and it's very much the opposite of beginner friendly.

The idea is that you configure your system in a configuration file, then run a command that makes your system match exactly what you configured.

So instead of apt install or similar you just add the package to your config, run a single command to rebuild the system and you're done.

Which also means you're mostly on your own, most guides for other distros don't work and the documentation on how to do the things in NixOS are very incomplete. It's nice and fun, but definitely not for an average user.