From Qt5 times we inherited CMake tests like the following in qtdeclarative/tests/auto/cmake/CMakeLists.txt:

set(module_includes "")

if(TARGET Qt::Qml)
    list(APPEND module_includes
        Qml QQmlEngine
    )
endif()

# ...

_qt_internal_test_module_includes(${module_includes})

This tests whether

• find_package(Qt6Qml 6.0.0 REQUIRED) is successful
• the Qt6Qml_VERSION variable and its MAJOR, MINOR, PATCH variants exist
• a test program linking against Qt6Qml can include <QtQml/QQmlEngine>
• said test program can instantiate a QQmlEngine object

All this is worth testing in a world where Qt is built with qmake and the creation of CMake support files relies on a correct setup of qmake project files per Qt module.

In Qt6, where Qt is built with CMake, this is essentially testing qt_internal_add_module and the underlying bits like

• syncqt creating the right forwarding headers
• CMake creating valid config packages per module
• the config packages containing the package version variables

I claim that this kind of test is not needed anymore, since this is covered by building dependent modules and examples with CMake. Therefore I suggest to remove these module include tests in every repository.