Alternatively, containers really are a no-thinking-required solution. Everything maximally isolated by default.
HVM hypervisors were doing stronger, safer, better isolation than Docker was 10 years ago. They are certainly no-thinking required though which leads to the abysmal state of containerized security and performance we have currently.
That's the thing, with NixOS you usually don't have to explicitly setup users and permissions. For most simple services, the entire setup is a single line of code in your NixOS configuration. E.g.
services.uptime-kuma.enable = true;
Some more complex software might require more configuration, but most of the time user and group setup is not part of that.