I would like to include one of the themes provided by the foot package in my ~/.config/foot/foot.ini.
I have installed foot, and foot.themes to get the extra output. I can locate the themes in the Nix store manually. Currently they are at /nix/store/q18dbs8354c7v5w1w2qbgll0iid1vq84-foot-1.16.2-themes/share/foot/themes/. But I failed to find a symbolic link to that path. I expected a link in /run/current-system/sw/share/.
You probably want to use home-manager. Nixos by itself will put the foot.ini file into the /nix/store, as you know since you were able to locate it there yourself.
Home-manager on the other hand will put the config file into the /nix/store and also symlink it to ~/.config/foot/foot.ini. While home-manager is not required, it’s extremely convenient and you’re likely to want to use it for other software as well.
Since you’ve already used a flake to install nixos, you can follow the instructions here: Home Manager Manual to add to that flake to get home-manager going. Home-manager is another nixos-module, that itself has a module system, but you don’t need to fully understand all of that yet to get going.
If you don’t want to use home-manager, you can set environment.pathsToLink = [ "share/foot" ], and that should get you where you want to be. (By default, only a subset of paths under installed package’s /share get linked under the system directory.)
Thanks for the hint. I’m hesitant to use Home Manager because I have existing cross platform dotfiles that I would like to use on NixOS as well for now.