To build my app for iOS I tried to run CMake from the command line without QT Creator:
cmake -S /Users/admin/dev/repos/examples/src/LinesGame/LinesGameQt -B . -DCMAKE_GENERATOR:STRING=Xcode \
-DCMAKE_PROJECT_INCLUDE_BEFORE:FILEPATH=./.qtc/package-manager/auto-setup.cmake -DQT_QMAKE_EXECUTABLE:FILEPATH=/Users/admin/dev/libs/QT6/release/iOS/bin/qmake6 \
-DCMAKE_PREFIX_PATH:PATH=/Users/admin/dev/libs/QT6/release/iOS \
-DCMAKE_C_COMPILER:FILEPATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang \
-DCMAKE_CXX_COMPILER:FILEPATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ \
-DCMAKE_TOOLCHAIN_FILE:FILEPATH=/Users/admin/dev/libs/QT6/release/iOS/lib/cmake/Qt6/qt.toolchain.cmake \
-DCMAKE_OSX_ARCHITECTURES:STRING=arm64 -DCMAKE_OSX_SYSROOT:STRING=iphoneos -DCMAKE_CXX_FLAGS_INIT:STRING= \
-DCMAKE_XCODE_ATTRIBUTE_DEVELOPMENT_TEAM:STRING=XXXXXXX