The current design pattern is as follows:
inside the clientAPI class, we have a function get_item which sends http get request.
when the responses is received, there is a signal from clinetAPI named signal_data emitting the data.
inside the mainWindow class we have the following:
we have a pointer of clientAPI named client as private member function in the mainWindow class. We have also a button get_btn, and a label as private member functions.
within the constructor of the mainWindow, we have two signal and slot connections. one connecting the clicked signal of get_btn to get_item function of client member function pointer.
In the other connection the signal signal_data from clinet is connected to the update_label slot of mainWindow.

My question is that if this design pattern is the common or right approach?
(note that in this design pattern I have clinet as a pointer inside the mainWindow class as the member function)
Should the design pattern be in different way. For example to have these two signal and slot connections in the main.cpp file and not inside the mainWindow.cpp. In other word, rather than having a client pointer as member function of the mainWindow, I make the two signal and slot connections inside the main.cpp.

Below I provide the code of clientAPI class which is common across the two appraoches and the code of two appraoches.

clientapi.cpp code:

#include "clientapi.h"

clientAPI::clientAPI(QObject *parent): QObject{parent}
{
    manager = new QNetworkAccessManager(this);
    QObject::connect(
        manager,
        &QNetworkAccessManager::finished,
        this,
        &clientAPI::reply_finished);
}

clientAPI::~clientAPI()
{
    delete(manager);
    qInfo() << "manager pointer was deleted.";
    qInfo() << this << "deconstructed";
}

void clientAPI::get_items()
{
    manager->get(QNetworkRequest(QUrl("http://127.0.0.1:8000/items/")));
    qInfo() << "get request was sent";
}

void clientAPI::reply_finished(QNetworkReply* _reply)
{
    QByteArray responses = _reply->readAll();
    QJsonDocument JsonDoc = QJsonDocument::fromJson(responses);
    QJsonArray JsonArray = JsonDoc.array();
    QString data = JsonArray.at(1)["title"].toString();
    emit data_received(data);
    _reply->deleteLater();
}

appraoch one :

code of MainWindow.cpp

#include "mainwindow.h"

MainWindow::MainWindow(clientAPI *_client, QWidget *parent): QMainWindow(parent), client(_client)
{
    get_btn = new QPushButton(this);
    test_label = new QLabel(this);

    get_btn->setGeometry(200,150, 80,40);
    get_btn->setText("register");

    test_label->setGeometry(300,150, 80,40);
    test_label->setText("...");
    test_label->setFrameStyle(QFrame::WinPanel | QFrame::Plain);

    //should I use test_label instead of this?!! && what is private slots, is public better.
    connect(get_btn, &QPushButton::clicked, client, &clientAPI::get_items);
    connect(client, &clientAPI::data_received, this, &MainWindow::update_label);

}

MainWindow::~MainWindow() = default;

void MainWindow::update_label(const QString _data)
{
    test_label->setText(_data);
}

main.cpp in appraoch 1 is :

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    clientAPI* client = new clientAPI();

    MainWindow w(client);
    w.show();
    return a.exec();
}

In appraoch 2, the MainWindow is as follow:

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent): QMainWindow(parent)
{
    get_btn = new QPushButton(this);
    test_label = new QLabel(this);

    get_btn->setGeometry(200,150, 80,40);
    get_btn->setText("register");

    test_label->setGeometry(300,150, 80,40);
    test_label->setText("...");
    test_label->setFrameStyle(QFrame::WinPanel | QFrame::Plain);

}

MainWindow::~MainWindow() = default;

void MainWindow::update_label(const QString _data)
{
    test_label->setText(_data);
}

QLabel *MainWindow::getTest_label() const
{
    return test_label;
}

void MainWindow::setTest_label(QLabel *newTest_label)
{
    test_label = newTest_label;
}

QPushButton *MainWindow::getGet_btn() const
{
    return get_btn;
}

void MainWindow::setGet_btn(QPushButton *newGet_btn)
{
    get_btn = newGet_btn;
}

and the main.cpp in the appraoch 2 is:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    clientAPI client();
    MainWindow w();
    QObject::connect(w.getGet_btn(), &QPushButton::clicked, &clinet, &clientAPI::get_items);
    QObject::connect(&client, &clientAPI::data_received, w.getTest_label(), &MainWindow::update_label);
    w.show();

    return a.exec();
}

Tanks a lot for your guide.
both of these approaches are working as I tested them, but I want your advice for designing a software, what approach you would choose? which one is more common and the right approach?
sorry of the question is long, let me know if I should make it shorter.