This project uses clipstudio-thumbnailer to make a thumbnailer for NixOS systems.

First check this, as you may need to modify environment.pathsToLink:

https://wiki.nixos.org/wiki/Thumbnails

Add this flake to your config, adding the package to your system packages

  environment.systemPackages = [
    inputs.clipstudio-thumbnailer.packages.${pkgs.stdenv.hostPlatform.system}.default
  ];

Then restart your thumbnailer service and file manager daemon, for example on Xfce:

systemctl --user restart tumblerd
pkill --signal SIGHUP thunar
thunar --daemon &