I use symlinks from configuration.nix and hardware -configuration.nix and point to specific instances for specific systems.

I have "if hostname == xyz" in my config, or I use a little config file with flags like "is_laptop".

There are a few solutions to this, but I keep separate configs for each device and link them into the entrypoint (/etc/nixos/configuration.nix) as-needed when I set things up. Then I have other "module" files for my terminal environment and my desktop environment, as well as an extra file that enables Wine/gaming packages.

In addition to the other suggestions, you can create different files for (e.g) each machine and use common includes for your apps and settings.

personally, the way I do it is:

/etc/nixos/roles/foo/default.nix has config for the 'foo' role (eg, I have a desktop role that enables all my GUI options)

configuration.nix and hardware-configuration.nix in /etc/nixos/ are symlinked to the actual files in /etc/nixos/hosts/<hostname>/

in the imports section of each machine's configuration.nix, I import /etc/nixos/roles/foo for each role the machine should use. for your graphics card example, I have 'nvidia' and 'nvidia470' roles that pull in their respective nvidia driver (due to an old gaming laptop that requires the legacy driver version)

I have a 'core' role that all machines import, with the global config I want on every host

this allows me to version-control my entire /etc/nixos directory (managed as a private git repo, replicated using syncthing rather than pushed to Github/Gitlab/etc). the symlinks in /etc/nixos are in .gitignore because they're machine-specific, and the actual per-host config files are able to be tracked in their own directories.

I use colmena[1] to manage one nixos configuration for multiple machines: - laptop - desktop - server - rpi nas

I also wipe my entire rootfs every boot with a zfs snapshot rollback[2] using the impermanence module[3] to keep specific stateful data one one of two datasets with regular snapshots: one is backed up with zfs send, the other is just for cache between reboots.

It took a little puzzling to get started, because I didn’t know about the impermanence module at first, so I built my own hacky solution. But I really love this setup. And the way I don’t have cruft to clean.

Also my backups are so much smaller now :’-)

[1]: https://colmena.cli.rs/

[2]: https://grahamc.com/blog/erase-your-darlings/

[3]: https://github.com/nix-community/impermanence

There are lots of ways to do this; pre-flakes e.g. you might have a root configuration file for each host which only includes other files, or have if statements.

Nix flakes lets you define as many configurations as you want, and (if you don't specify one) will select based on the hostname.