How to alter OSX_DEPLOYMENT_TARGET for a specific target in CMake for xcode project

For make project, the below minimal example will allow me to alter OSX_DEPLOYMENT_TARGET for a specific target successfully:

set(CMAKE_OSX_DEPLOYMENT_TARGET
    "11.0"
    CACHE STRING "osx deployment target")

# the osx deployment target of mylib is 11.0
add_subdirectory(mylib)

# but one of the external library the test links to is built with 12.0, so I want the test to be compiled with 12.0
find_package(external)

set_property(
  TARGET external
  APPEND
  PROPERTY INTERFACE_COMPILE_OPTIONS -mmacosx-version-min=12.0
  PROPERTY INTERFACE_LINK_OPTIONS -mmacosx-version-min=12.0)

add_executable(mytest main.cpp)

target_link_libraries(mytest PUBLIC mylibs external)

However, for xcode project, the OSX_DEPLOYMENT_TARGET is controlled by -target x86_64-apple-macos12.0 and -target arm64-apple-macos12.0. mytest is a universal binary with x86_64 and arm64, and I am having difficulties to figure out how to pass -target x86_64-apple-macos12.0 to the x86_64 slice and -target arm64-apple-macos12.0 to the arm64 slice in cmake. My best attempt looks like the below:

set_property(
  TARGET external
  APPEND
  PROPERTY
    INTERFACE_COMPILE_OPTIONS
    -target
    $<$<STREQUAL:$<TARGET_PROPERTY:OSX_ARCHITECTURES>,x86_64:x86_64-apple-macos12.0>>
    $<$<STREQUAL:$<TARGET_PROPERTY:OSX_ARCHITECTURES>,arm64:arm64-apple-macos12.0>>
  PROPERTY
    INTERFACE_LINK_OPTIONS
    -target
    $<$<STREQUAL:$<TARGET_PROPERTY:OSX_ARCHITECTURES>,x86_64:x86_64-apple-macos12.0>>
    $<$<STREQUAL:$<TARGET_PROPERTY:OSX_ARCHITECTURES>,arm64:arm64-apple-macos12.0>>
)

but unfortunately this doesn't work. A more general question is that how can I pass in different compilation flags when compiling different archs?

You seem to be looking for CMAKE_OSX_ARCHITECTURES:

cmake ... -DCMAKE_OSX_ARCHITECTURES=arm64

or

set(CMAKE_OSX_ARCHITECTURES arm64)

> how can I pass in different compilation flags when compiling different archs?

Xcode/xcodebuild can't do it. You have to build single arch targets and merge them with lipo -create -output universal_app x86_app arm_app.

I found the answer from https://github.com/eyalamirmusic/JUCECmakeRepoPrototype/issues/5#issuecomment-747082201.

It's set_target_properties(mytest PROPERTIES XCODE_ATTRIBUTE_MACOSX_DEPLOYMENT_TARGET 12.0)