Earlier quoted context omitted.
> but I cannot live without NixOS, Just to double check: nix on Darwin isn't good enough?
Nope. I tried it and hated the MacOS GUI. I like my window-manager config, and various other deep customizations. Also, MacOS updates kept breaking things.
Nix-Darwin (the module system that gives you some NixOS-like features with Nix on macOS) is nice, but macOS ultimately can't match the predictability and control one gets used to on NixOS. A system that updates in a non-uniform way, has limited configurability, and where the configuration of the system isn't given anywhere in a trackable, comprehensible form feels painfully chaotic in comparison.
(I can understand why Nix on Darwin (with or without Nix-Darwin) is a great fit for many, though. Having a 'normal', mainstream desktop underneath your still relatively predictable, explicit, reproducible dev tooling is awesome in a lot of ways.)