Ошибки в Qt Creator: no member named 'setModal', no member named 'exec'

Создал два окна: mainwindow и settings, при нажатии кнопки в mainwindow должно открываться окно settings, делал один в один, как в видеоуроке и ничего не работает.

settings.h

#ifndef SETTINGS_H
#define SETTINGS_H

#include <QMainWindow>

namespace Ui {
class Settings;
}

class Settings : public QMainWindow
{
    Q_OBJECT

public:
    explicit Settings(QWidget *parent = nullptr);
    ~Settings();

private:
    Ui::Settings *ui;
};

#endif // SETTINGS_H

settings.cpp

#include "settings.h"
#include "ui_settings.h"

Settings::Settings(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::Settings)
{
    ui->setupUi(this);
}

Settings::~Settings()
{
    delete ui;
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void on_actionSettings_clicked();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "settings.h"
   

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}


void MainWindow::on_actionSettings_clicked()
{
    Settings settings;
    settings.setModal(true);   error: no member named 'setModal' in 'Settings'
    settings.exec();           error: no member named 'exec' in 'Settings'             
}