Webengine examples fails to build: undefined reference to `QApplication::QApplication(int&, char**, int)'

[3/3] Linking CXX executable customdialogs
FAILED: customdialogs 
: && /usr/bin/c++   CMakeFiles/customdialogs.dir/customdialogs_autogen/mocs_compilation.cpp.o CMakeFiles/customdialogs.dir/main.cpp.o CMakeFiles/customdialogs.dir/server.cpp.o CMakeFiles/customdialogs.dir/.rcc/qrc_customdialogs.cpp.o -o customdialogs  -Wl,-rpath,/home/johanna/RTA/qt5/6.2.0/gcc_64/lib:  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6WebEngineQuick.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6WebEngineCore.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6Quick.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6QmlModels.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6OpenGL.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6Gui.so.6.2.0  /usr/lib/x86_64-linux-gnu/libGLX.so  /usr/lib/x86_64-linux-gnu/libOpenGL.so  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6WebChannel.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6Qml.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6Network.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6Positioning.so.6.2.0  /home/johanna/RTA/qt5/6.2.0/gcc_64/lib/libQt6Core.so.6.2.0  -pthread && :
/usr/bin/ld: CMakeFiles/customdialogs.dir/main.cpp.o: in function `main':
main.cpp:(.text+0x161): undefined reference to `QApplication::QApplication(int&, char**, int)'
/usr/bin/ld: main.cpp:(.text+0x2b8): undefined reference to `QApplication::exec()'
/usr/bin/ld: main.cpp:(.text+0x2e2): undefined reference to `QApplication::~QApplication()'
/usr/bin/ld: main.cpp:(.text+0x3c1): undefined reference to `QApplication::~QApplication()'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.