

Nix and Docker / container runtimes are completely different animals. Each is good at what they do, but those are vastly different things, with some overlap. If you want to share a kernel but use fewer resources than a VM, containers can do that. If you want to go further and completely isolate, you can use microvm’s like firecracker.
I don’t follow what is wrong with that. Maybe you mean it’s use where people use it specifically as a package manager. I agree with that, but even then it has its handy place.
I quasi-journal at work, just to remember what I’ve done and why I did it. I do so using markdown files.