NixOS packages only work with NixOS system. They’re harder to setup than just copying a docker-compose file over and they do use container technology.

It's interesting how none of that is true.

Nixpkgs work on practically any Linux kernel.

Whether NixOS modules are easier to set up and maintain than unsustainably copying docker-compose files is subjective.

Neither Nixpkgs nor NixOS use container technology for their core functionality.
NixOS has the nixos-container framework to optionally run NixOS inside of containerised environments (systemd-nspawn) but that's rather niche actually. Nixpkgs does make use of bubblewrap for a small set of stubborn packages but it's also not at all core to how it works.

Totally beside the point though; even if you don't think NixOS is simpler, that still doesn't mean containers are the only possible mean by which you could possibly achieve "easy" deployments.

Also without containers you don’t solve the biggest problems such as incompatible database versions between multiple services.

Ah, so you have indeed not even done the bare minimum of research into what Nix/NixOS are before you dismissed it. Nice going there.

as robust in terms of configurations

Docker compose is about the opposite of a robust configuration system.