Unable to assing [undefined] to QString

[ROS2 Humble with QML]

I have encountered a problem that I have been trying to avoid for months. It is that I cannot assign a variable that I get from outside QML, that is, in the backend with C++ and it is giving me errors when assigning an external variable to something within QML. I will show you the entire program below.
main.cpp:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <stringHandler.h>

int main(
    int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    StringHandler stringHandler;
    stringHandler.loadData();
    engine.rootContext()->setContextProperty("stringHandler", &stringHandler);

    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreationFailed,
        &app,
        []() { QCoreApplication::exit(-1); },
        Qt::QueuedConnection);
    engine.loadFromModule("untitled4", "Main");

    return app.exec();
}

stringHandler.h:

#ifndef STRINGHANDLER_H
#define STRINGHANDLER_H
#include <QObject>
#include <QStringListModel>
#include <vector>
#include <string>
#include <QQmlContext>


class StringHandler : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QStringListModel* model READ model NOTIFY modelChanged)

public:
    explicit StringHandler(QObject *parent = nullptr) : QObject(parent), m_model(new QStringListModel(this)) {}

    QStringListModel *model() const{
        return m_model;
    }

    Q_INVOKABLE void loadData() {
        QStringList list;
        const std::vector<std::string> data = {"Mapa 1", "Mapa 2", "Mapa 3"};
        for (const std::string &str : data) {
            qDebug() << "Loading: " << QString::fromStdString(str);  // Depuración
            list.append(QString::fromStdString(str));
        }
        m_model->setStringList(list);
        emit modelChanged();  // Notificar a QML
    }

signals:
    void modelChanged();

private:
    QStringListModel *m_model;
};

#endif // STRINGHANDLER_H

Main.qml

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15

Window {
    // width: 640
    // height: 480
    visible: true
    title: qsTr("Hello World")
    Rectangle {
        visible: true
        width: 500
        height: 400

        // ScrollView para contener el ListView
        ScrollView {
            anchors.fill: parent
            clip: true

            // ListView para mostrar los elementos
            ListView {
                id: listView
                model: stringHandler.model  // Modelo que se enlaza con el StringHandler de C++

                delegate: Item {
                    width: listView.width
                    height: 70

                    Rectangle {
                        width: parent.width
                        height: 60
                        color: "#ffffff"
                        border.color: "#cccccc"
                        radius: 10

                        Row {
                            anchors.fill: parent
                            spacing: 20
                            anchors.margins: 10

                            Text {
                                text: modelData  // Se accede al modelo de datos
                                font.pixelSize: 18
                                color: "#000000"
                                anchors.verticalCenter: parent.verticalCenter
                            }

                            Button {
                                text: "Editar"
                                anchors.verticalCenter: parent.verticalCenter
                                onClicked: console.log("Editar", modelData)
                            }

                            Button {
                                text: "Borrar"
                                anchors.verticalCenter: parent.verticalCenter
                                onClicked: console.log("Borrar", modelData)
                            }
                        }
                    }
                }
            }
        }
    }
}

The output:

QML debugging is enabled. Only use this in a safe environment.
Loading:  "Mapa 1"
Loading:  "Mapa 2"
Loading:  "Mapa 3"
qrc:/qt/qml/untitled4/Main.qml:42:33: Unable to assign [undefined] to QString
qrc:/qt/qml/untitled4/Main.qml:42:33: Unable to assign [undefined] to QString
qrc:/qt/qml/untitled4/Main.qml:42:33: Unable to assign [undefined] to QString
qrc:/qt/qml/untitled4/Main.qml:23: TypeError: Cannot read property 'model' of null

CMakeLists.txt:

cmake_minimum_required(VERSION 3.16)

project(untitled4 VERSION 0.1 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 REQUIRED COMPONENTS Quick)

qt_standard_project_setup(REQUIRES 6.5)

qt_add_executable(appuntitled4
    main.cpp
)

qt_add_qml_module(appuntitled4
    URI untitled4
    VERSION 1.0
    QML_FILES
        Main.qml
        SOURCES stringHandler.h
)

# Qt for iOS sets MACOSX_BUNDLE_GUI_IDENTIFIER automatically since Qt 6.1.
# If you are developing for iOS or macOS you should consider setting an
# explicit, fixed bundle identifier manually though.
set_target_properties(appuntitled4 PROPERTIES
#    MACOSX_BUNDLE_GUI_IDENTIFIER com.example.appuntitled4
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

target_link_libraries(appuntitled4
    PRIVATE Qt6::Quick
)

include(GNUInstallDirs)
install(TARGETS appuntitled4
    BUNDLE DESTINATION .
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

I have the same problem when i use a .qml as a header where I have all the constanst

recommendation I'm all ears thank you very much

[dheerendra]

Use default role display for QStringListModel like this,

                        Text {
                            text: display  // Se accede al modelo de datos
                            font.pixelSize: 18
                            color: "#000000"
                            anchors.verticalCenter: parent.verticalCenter
                        }

[ROS2 Humble with QML]

Amazing thank you very much ^^