Apart from dd you can also go for Clonezilla or Rescuezilla. Both not super user friendly but once you get familiar with it makes backups and restore easy and fast for data and boot-loader.

If you like NixOS for its packages, you can install a Systemd free OS, and then add Nix package manager. For example Nix-bin is packaged for Debian and the Systemd free Devuan : https://pkginfo.devuan.org/cgi-bin/policy-query.html?c=package&q=nix-bin&x=submit Here is a very old howto for Void Linux, but maybe still works : https://voidlinux.org/news/2014/01/Using-the-Nix-package-manager.html