Qt5 and Cmake linking QApplication header error

I am trying to link cmake with one of my Qt projects that uses QApplication. I am getting this error when I build the project

Cannot open include file: 'QApplication': No such file or directory

I am only using QApplication and QWebEngineWidget in my .cpp file and QDir in the header file

main.h

#ifndef MAIN_H
#define MAIN_H

#include <QDir>

QUrl getlink(){

    QUrl url = QUrl::fromLocalFile(QDir::currentPath();

    return url;

}


#endif // MAIN_H

main.cpp

    #include <QApplication>
    #include <QWebEngineView>
    #include "main.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QApplication app(argc, argv);

    QWebEngineView view;
    view.setUrl(getlink());
    view.resize(1524, 850);
    view.show();

   return app.exec();

}

and here is the code from my CMake file for this application

if (ENABLE_QT_SimApp_GUI)

find_package(qtlibs)

find_package(SimApp)
if (NOT SimApp_FOUND)
    message(FATAL_ERROR "Could not find SimApp")
endif(NOT SimApp_FOUND)

set(CMAKE_PREFIX_PATH ${PREFIX_PATH})
message(STATUS "CMAKE_PREFIX_PATH" ${CMAKE_PREFIX_PATH})

find_package(Qt5 REQUIRED COMPONENTS Widgets Core Gui Sql PrintSupport WebEngineWidgets)

qt5_wrap_cpp(QtSimAppProjectLib_hdr_moc ${QtSimAppProjectLib_hdr})
qt5_wrap_ui(QtSimAppProjectLib_ui_uic ${QtSimAppProjectLib_ui})
qt5_add_resources(QtSimAppProjectLib_qrc_rcc ${QtSimAppProjectLib_qrc})

include_directories (${PROJECT_SOURCE_DIR})
include_directories (${PROJECT_BINARY_DIR})

add_library (QtSimAppProjectLib STATIC ${QtSimAppProjectLib_src} ${QtSASQProjectLib_hdr_moc} ${QtSASQProjectLib_ui_uic})

target_link_libraries (QtSimAppProjectLib
        Qt5::Core
        Qt5::Gui
        Qt5::Widgets
        Qt5::Sql
        Qt5::PrintSupport
        Qt5::WebEngineWidgets)

#WIN32 to suppress the console window under Windows
add_executable(SIM_APP WIN32 ${QtSimAppProjectLib_src} ${QtSimAppProjectLib_qrc_rcc})

    if (ENABLE_COPY_QT_LIBS AND WIN32)
        find_package(qtdlls)
    endif(ENABLE_COPY_QT_LIBS AND WIN32)

endif (ENABLE_QT_SimApp_GUI)

I am aware that I may not need the other linked libs but I kept them there for future development.

Anyway, when I added Qt5::WebEngineWidget for QWebEngineView in the target link it worked fine, but when I added Qt5::Widgets for QApplication it does not seem to be able to find the file and i dont know why.

Any idea on what could be the issue?

As mentioned in the comments by @vre , you never actually link your GUI app to Qt5. Below is a fixed version of your posted CMakeLists.txt

if (ENABLE_QT_SimApp_GUI)

find_package(qtlibs)

find_package(SimApp)
if (NOT SimApp_FOUND)
    message(FATAL_ERROR "Could not find SimApp")
endif(NOT SimApp_FOUND)

set(CMAKE_PREFIX_PATH ${PREFIX_PATH})
message(STATUS "CMAKE_PREFIX_PATH" ${CMAKE_PREFIX_PATH})

find_package(Qt5 REQUIRED COMPONENTS Widgets Core Gui Sql PrintSupport WebEngineWidgets)

qt5_wrap_cpp(QtSimAppProjectLib_hdr_moc ${QtSimAppProjectLib_hdr})
qt5_wrap_ui(QtSimAppProjectLib_ui_uic ${QtSimAppProjectLib_ui})
qt5_add_resources(QtSimAppProjectLib_qrc_rcc ${QtSimAppProjectLib_qrc})

include_directories (${PROJECT_SOURCE_DIR})
include_directories (${PROJECT_BINARY_DIR})

add_library (QtSimAppProjectLib STATIC ${QtSimAppProjectLib_src} ${QtSASQProjectLib_hdr_moc} ${QtSASQProjectLib_ui_uic})

target_link_libraries (QtSimAppProjectLib
        Qt5::Core
        Qt5::Gui
        Qt5::Widgets
        Qt5::Sql
        Qt5::PrintSupport
        Qt5::WebEngineWidgets)

#WIN32 to suppress the console window under Windows
add_executable(SIM_APP WIN32 ${QtSimAppProjectLib_src} ${QtSimAppProjectLib_qrc_rcc})

# use one of the following target_link_libraries() calls
target_link_libraries(SIM_APP Qt5::Core Qt5::Gui Qt5::Widgets)
# target_link_libraries(SIM_APP QtSimAppProjectLib)

if (ENABLE_COPY_QT_LIBS AND WIN32)
    find_package(qtdlls)
endif(ENABLE_COPY_QT_LIBS AND WIN32)

endif (ENABLE_QT_SimApp_GUI)