Very bare flake example using the image builder for the dynalink_dl-wrx36 access point.

flake.nix

{
  inputs = {
    openwrt-imagebuilder.url = "github:astro/nix-openwrt-imagebuilder";
  };
  outputs = { self, nixpkgs, openwrt-imagebuilder }: {
    packages.x86_64-linux.ap1 =
      let
        pkgs = nixpkgs.legacyPackages.x86_64-linux;

        profiles = openwrt-imagebuilder.lib.profiles { inherit pkgs; };

        config = profiles.identifyProfile "dynalink_dl-wrx36" // {
          packages = [ "wpad-mbedtls" "acme-acmesh-dnsapi" "dawn" "ddns-scripts-cloudflare" "-wpad-basic-mbedtls" ];
          disabledServices = [ "dnsmasq" ];
          # official OpenWRT ImageBuilder recommendation.
          files = pkgs.runCommand "image-files" {} ''
            mkdir -p $out/etc/uci-defaults
            cat > $out/etc/uci-defaults/99-custom <<EOF
            uci -q batch << EOI
            set system.@system[0].hostname='testap'
            commit
            EOI
            EOF
          '';
        };

      in
        openwrt-imagebuilder.lib.build config;
  };
}

Used via nix run .#packages.x86_64-linux.ap1.
Output:

ls result/
nix-support
openwrt-23.05.0-ipq807x-generic-dynalink_dl-wrx36.manifest
openwrt-23.05.0-ipq807x-generic-dynalink_dl-wrx36-squashfs-factory.ubi
openwrt-23.05.0-ipq807x-generic-dynalink_dl-wrx36-squashfs-sysupgrade.bin
profiles.json
sha256sums