How should I add Qt private headers to my CMakeLists.txt ?
find_package(QT NAMES Qt6 Qt5 COMPONENTS Core Quick QuickPrivate REQUIRED)
find_package(Qt${QT_VERSION_MAJOR} COMPONENTS Core Quick QuickPrivate REQUIRED)
If you want to use the private API of the "QTMOD" submodule then you must include only the headers using the variable:
Qt${QT_VERSION_MAJOR}QTMOD_INCLUDE_DIRS
In your case:
include_directories(${Qt${QT_VERSION_MAJOR}Quick_PRIVATE_INCLUDE_DIRS})
Note: Not exist QuickPrivate