gn.py needs an -isysroot argument but configure doesn't create it

% xcodebuild -version && xcodebuild -showsdks
Xcode 16.3
Build version 16E140
DriverKit SDKs:
    DriverKit 24.4                    -sdk driverkit24.4
iOS SDKs:
    iOS 18.4                          -sdk iphoneos18.4
iOS Simulator SDKs:
    Simulator - iOS 18.4              -sdk iphonesimulator18.4
macOS SDKs:
    macOS 15.4                        -sdk macosx15.4
    macOS 15.4                        -sdk macosx15.4
tvOS SDKs:
    tvOS 18.4                         -sdk appletvos18.4
tvOS Simulator SDKs:
    Simulator - tvOS 18.4             -sdk appletvsimulator18.4
visionOS SDKs:
    visionOS 2.4                      -sdk xros2.4
visionOS Simulator SDKs:
    Simulator - visionOS 2.4          -sdk xrsimulator2.4
watchOS SDKs:
    watchOS 11.4                      -sdk watchos11.4
watchOS Simulator SDKs:
    Simulator - watchOS 11.4          -sdk watchsimulator11.4

% xcrun --show-sdk-path                                                                            
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk

../qt6/configure LLVM_INSTALL_DIR=/opt/homebrew/opt/llvm FEATURE_clang=ON -developer-build -nomake tests  -nomake examples -sbom 

[236/11949] Performing build step for 'gn'
[0/1] Generating gn
usage: gen.py [-h] [-d] [--platform {linux,darwin,mingw,msys,msvc,aix,fuchsia,freebsd,netbsd,openbsd,haiku,solaris,zos,serenity}]
              [--host {linux,darwin,mingw,msys,msvc,aix,fuchsia,freebsd,netbsd,openbsd,haiku,solaris,zos,serenity}] [--use-lto] [--use-icf] [--use-asan] [--use-ubsan]
              [--no-last-commit-position] [--out-path OUT_PATH] [--no-strip] [--no-static-libstdc++] [--link-lib LINK_LIB] [--allow-warnings] [--cc CC] [--cxx CXX] [--ld LD] [--ar AR]
              [--isysroot ISYSROOT] [--qt-version QT_VERSION] [--osx-architectures OSX_ARCHITECTURES] [--gcc-legacy-support]
gen.py: error: argument --isysroot: expected one argument
FAILED: gn /Users/jpasion/code/build-qt6/qtwebengine/src/gn/gn 
cd /Users/jpasion/code/build-qt6/qtwebengine/src/gn && /opt/homebrew/Frameworks/Python.framework/Versions/3.13/bin/python3.13 /Users/jpasion/code/qt6/qtwebengine/src/3rdparty/gn/build/gen.py --no-last-commit-position --no-static-libstdc++ --out-path /Users/jpasion/code/build-qt6/qtwebengine/src/gn/Release --cc /usr/bin/cc --cxx /usr/bin/c++ --ld /usr/bin/c++ --allow-warnings --platform darwin --ar /usr/bin/ar --qt-version 6.10.0.qtwebengine.qt.io --isysroot && /opt/homebrew/bin/ninja -C /Users/jpasion/code/build-qt6/qtwebengine/src/gn/Release gn
ninja: build stopped: subcommand failed.
[238/11949] Building CXX object qtquick3dphysics/src/3rdparty/PhysX/CMakeFiles/BundledPhysX.dir/source/geomutils/src/contact/GuContactCapsuleBox.cpp.o
FAILED: qtwebengine/src/gn/src/gn-stamp/gn-build /Users/jpasion/code/build-qt6/qtwebengine/src/gn/src/gn-stamp/gn-build 
cd /Users/jpasion/code/build-qt6/qtwebengine/src/gn && /opt/homebrew/bin/cmake --build . && /opt/homebrew/bin/cmake -E touch /Users/jpasion/code/build-qt6/qtwebengine/src/gn/src/gn-stamp/gn-build
[248/11949] Building OBJCXX object qtbase/src/corelib/CMakeFiles/Core.dir/platform/darwin/qdarwinpermissionplugin.mm.o
ninja: build stopped: subcommand failed.