Ansible makes mutable changes to the OS, task by task.

Nix is immutable. A new change is made entirely new, and only after the build is successful, all packages are "symlinked" to the current system.

Fedora Silverblue is based on ostree [1]. It works similarly like git, but on your root tree. But it requires you to reboot the whole system for the changes to take effect. Since Nix is just symlinked packages, you don't need to reboot the system.

More detailed explanation here [2].

[1]: https://github.com/ostreedev/ostree

[2]: https://dataswamp.org/~solene/2023-07-12-intro-to-immutable-...