Below observation of the Car build
AOSP using the "Settings" app source path:
Path: AA11/android_build/packages/apps/Settings/src/com/android/settings/network

AAOS build using the Car "Settings" app
Path: AA11/android_build/packages/apps/Car/Settings/src/com/android/car/settings/network

Can you please give support us to AOSP settings app to be installed instead of the AA11 (Car Settings) app, then we can get the "Mobile Network" option enabled in the Settings App for the Automotive car build.