Error when cross-compiling for iOS with XCode13

[cristeab]

Hi
I am trying to cross-compile for iOS an application build with Qt5.15.2.When I try to compile with make I get the error below:

codebuild build -project Monitor.xcodeproj -scheme Monitor -configuration Release -destination generic/platform=iOS -destination-timeout 1 ENABLE_ONLY_ACTIVE_RESOURCES=NO
Command line invocation:
/Applications/Xcode.app/Contents/Developer/usr/bin/xcodebuild build -project Monitor.xcodeproj -scheme Monitor -configuration Release -destination generic/platform=iOS -destination-timeout 1 ENABLE_ONLY_ACTIVE_RESOURCES=NO

User defaults from command line:
IDEPackageSupportUseBuiltinSCM = YES

Build settings from command line:
ENABLE_ONLY_ACTIVE_RESOURCES = NO

Prepare build
error: The Legacy Build System will be removed in a future release. You can configure the selected build system and this deprecation message in File > Project Settings.
Build Preparation
The Legacy Build System will be removed in a future release. You can configure the selected build system and this deprecation message in File > Project Settings.

** BUILD FAILED **

I can solve this error by opening the generated Xcode project and changing in File -> Project Settings ... the Build System to "New Build System (Default)", then I recompile again with make. Is there an option in qmake that allows to specify the new build system ?

thanks
Bogdan