Cmake: Could NOT find Python (missing: Python_EXECUTABLE Interpreter)

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I’m using vcpkg to get the qtdeclarative port (Qt 6.8.2), but I keep getting the following error when compiling.

CMake Error at /nix/store/xh4gd0g8j4sfwb4gg164a2hc22i0b7jh-cmake-3.31.5/share/cmake-3.31/Modules/FindPackageHandleStandardArgs.cmake:233 (message):
  Could NOT find Python (missing: Python_EXECUTABLE Interpreter)
Call Stack (most recent call first):
  /nix/store/xh4gd0g8j4sfwb4gg164a2hc22i0b7jh-cmake-3.31.5/share/cmake-3.31/Modules/FindPackageHandleStandardArgs.cmake:603 (_FPHSA_FAILURE_MESSAGE)
  /nix/store/xh4gd0g8j4sfwb4gg164a2hc22i0b7jh-cmake-3.31.5/share/cmake-3.31/Modules/FindPython.cmake:673 (find_package_handle_standard_args)
  /nix/store/wh6jyld823x0zbr1a71ir6xnf3fajwl1-vcpkg-2025.02.14/share/vcpkg/scripts/buildsystems/vcpkg.cmake:859 (_find_package)
  /Users/denniseum/Projects/internal/cs2620/converse/exe_client/build/vcpkg_installed/arm64-osx/share/Qt6/QtFindPackageHelpers.cmake:141 (find_package)
  src/qml/configure.cmake:14 (qt_find_package)
  /Users/denniseum/Projects/internal/cs2620/converse/exe_client/build/vcpkg_installed/arm64-osx/share/Qt6/QtFeature.cmake:678 (include)
  src/qml/CMakeLists.txt:13 (qt_feature_evaluate_features)

I tried checking with

cmake_minimum_required(VERSION 3.30)

find_package(
  Python
  COMPONENTS Interpreter Development
  REQUIRED)

message(STATUS "Python Interpreter: ${Python_EXECUTABLE}")
message(STATUS "Python Version: ${Python_VERSION}")
message(STATUS "Python Include Dir: ${Python_INCLUDE_DIRS}")
message(STATUS "Python Library: ${Python_LIBRARIES}")

but that resolves correctly with

-- Found Python: /nix/store/3p3agnh4792y8bgjp0s8xx5bym1ahpks-python3-3.12.9/bin/python3.12 (found version "3.12.9") found components: Interpreter Development Development.Module Development.Embed
-- Python Interpreter: /nix/store/3p3agnh4792y8bgjp0s8xx5bym1ahpks-python3-3.12.9/bin/python3.12
-- Python Version: 3.12.9
-- Python Include Dir: /nix/store/3p3agnh4792y8bgjp0s8xx5bym1ahpks-python3-3.12.9/include/python3.12
-- Python Library: /nix/store/3p3agnh4792y8bgjp0s8xx5bym1ahpks-python3-3.12.9/lib/libpython3.12.dylib

The flake I am using is

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };
  outputs =
    { self, nixpkgs }:
    let
      system = "aarch64-darwin";
      pkgs = import nixpkgs {
        inherit system;
      };
    in
    {
      devShells.${system}.default = pkgs.mkShell {
        buildInputs = with pkgs; [
          apple-sdk_15
        ];
        nativeBuildInputs = with pkgs; [
          autoconf
          autoconf-archive
          automake
          cmake
          cups
          libtool
          llvmPackages_20.clang-tools
          llvmPackages_20.clangWithLibcAndBasicRtAndLibcxx
          ninja
          perl
          python3
          pkg-config
          vcpkg
          zlib
        ];
        shellHook = ''
          export VCPKG_ROOT=${pkgs.vcpkg}/share/vcpkg
          export VCPKG_FORCE_SYSTEM_BINARIES=1
        '';
      };
    };
}

Does this have something to do with Nix’s isolation? I’ve tried setting Python_EXECUTABLE and PYTHON_EXECUTABLE when calling cmake, but it makes no difference when compiling qtdeclarative.