gistfile1.txt

  hardware.deviceTree.filter = "bcm2708-rpi-zero*.dtb";
  hardware.deviceTree.overlays = [{
    name = "dwc2";
    dtboFile = "${pkgs.device-tree_rpi.overlays}/dwc2.dtbo";
  } # <<< Doesn't work
  {
    name = "hifiberry-dac";
    dtboFile = "${pkgs.device-tree_rpi.overlays}/hifiberry-dac.dtbo";
  } # <<< works
];

 sdImage = {
    populateFirmwareCommands = let
      configTxt = pkgs.writeText "config.txt" ''
        # Prevent the firmware from smashing the framebuffer setup done by the mainline kernel
        # when attempting to show low-voltage or overtemperature warnings.
        avoid_warnings=1
        [pi0]
        kernel=u-boot-rpi0.bin
        [pi1]
        kernel=u-boot-rpi1.bin
      '';
      in ''
        (cd ${pkgs.raspberrypifw}/share/raspberrypi/boot && cp bootcode.bin fixup*.dat start*.elf $NIX_BUILD_TOP/firmware/)
        cp ${pkgs.ubootRaspberryPiZero}/u-boot.bin firmware/u-boot-rpi0.bin
        cp ${pkgs.ubootRaspberryPi}/u-boot.bin firmware/u-boot-rpi1.bin
        cp ${configTxt} firmware/config.txt
      '';
    populateRootCommands = ''
      mkdir -p ./files/boot
      ${config.boot.loader.generic-extlinux-compatible.populateCmd} -c ${config.system.build.toplevel} -d ./files/boot
    '';
  };

gistfile2.txt

these derivations will be built:
  /nix/store/127kpw4sflvmpfpl715wdd4pqpr4pm57-device-tree-overlays.drv
  /nix/store/73g1rv9d91l6mk70snwjfy5nffs6n7q1-nixos-system-igor-rpizero-21.05pre-git.drv
  /nix/store/kmyzwxqcc5armwinwh7fvggkv3mm3xaj-closure-info.drv
  /nix/store/zpq0mya5z1i3a2yc47shfk34iirxp6ip-ext4-fs.img.zst-armv6l-unknown-linux-gnueabihf.drv
  /nix/store/khvwy09m4nyjlgzcv10v27ygv0vwx7kw-nixos-sd-image-21.05pre-git-armv6l-linux.img-armv6l-unknown-linux-gnueabihf.drv
building '/nix/store/127kpw4sflvmpfpl715wdd4pqpr4pm57-device-tree-overlays.drv'...
'./bcm2708-rpi-zero-w.dtb' -> '/nix/store/xr5g7cy14kakdcc8k8ljkbkdlk32awb5-device-tree-overlays/./bcm2708-rpi-zero-w.dtb'
'./bcm2708-rpi-zero.dtb' -> '/nix/store/xr5g7cy14kakdcc8k8ljkbkdlk32awb5-device-tree-overlays/./bcm2708-rpi-zero.dtb'
Applying overlay dwc2 to bcm2708-rpi-zero-w.dtb

Failed to apply '/nix/store/jq3cr9l1gj6gisb60wddab6x83gg0rb6-raspberrypi-firmware-1.20201201/share/raspberrypi/boot/overlays/dwc2.dtbo': FDT_ERR_NOTFOUND
builder for '/nix/store/127kpw4sflvmpfpl715wdd4pqpr4pm57-device-tree-overlays.drv' failed with exit code 1
cannot build derivation '/nix/store/73g1rv9d91l6mk70snwjfy5nffs6n7q1-nixos-system-igor-rpizero-21.05pre-git.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/kmyzwxqcc5armwinwh7fvggkv3mm3xaj-closure-info.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/zpq0mya5z1i3a2yc47shfk34iirxp6ip-ext4-fs.img.zst-armv6l-unknown-linux-gnueabihf.drv': 2 dependencies couldn't be built
cannot build derivation '/nix/store/khvwy09m4nyjlgzcv10v27ygv0vwx7kw-nixos-sd-image-21.05pre-git-armv6l-linux.img-armv6l-unknown-linux-gnueabihf.drv': 1 dependencies couldn't be built
error: build of '/nix/store/khvwy09m4nyjlgzcv10v27ygv0vwx7kw-nixos-sd-image-21.05pre-git-armv6l-linux.img-armv6l-unknown-linux-gnueabihf.drv' failed