Qt 6.9.3, 6.10.1 on Mac: QMAKE_APPLE_DEVICE_ARCHS="arm64" but QT_ARCH reports "x86_64"

[Violet Giraffe]

I'm building for arm64:
/Users/me/Qt/6.10.1/macos/bin/qmake -o Makefile /Users/me/project/lib/lib.pro CONFIG+=debug CONFIG+=qml_debug -spec macx-clang QMAKE_APPLE_DEVICE_ARCHS=arm64

But message($$QT_ARCH) prints "x86_64", why??
MacOS 26.1, the latest Xcode is insalled from App Store, command line tools were updated after updating Xcode.

lipo -info mylib.a says it was actually compiled for x86_64 despite the flag saying arm64, and this flag (-arch arm64) is present on the clang command line.

[SGaist]

Hi,

What architecture is your build machine ?

[Violet Giraffe]

Hi, happy New Year!
It's M1. I can't build a working app on M1 at all, neither for x64 nor for arm64, and I suspect something is malfunctioning (as opposed to just wrong project settings). It might be new with the recent Xcode update a few weeks ago.

[Violet Giraffe]

Does anyone have any advice on how to properly select your target architecture with the latest Xcode+macOS+Qt versions?