Qt6.8.2 iOS: Keyboard invisible in the background

TheoSys

I wrote a small application in C++ and compiled it now with qt 6.8.2. When I developed the app I used Qt 6.7.3. With this version everything worked as expected.
My app displays on startup a small dialog (QDialog) with 2 input lines and an OK button. When I tap to the first input line the cursor appears but no keyboard. But when I tap on the screen where the keyboard should be, the letters appearing in the input line. How can I bring the keyboard in forground? Or should I try to bring the app into the background?

Here is a code snipped showing how the dialog is called:

bool THeating::login()
{
    qDebug() << "DEBUG: THeating::login()";

    TLogin *login = new TLogin(mParent);

    if (login->exec() == QDialog::Accepted)
    {
        mUser = login->getUser();
        QString requestAuth = login->askForPermission();

        if (requestAuth.length() == 0)
        {
            QMessageBox::critical(mParent, "THeating", tr("Ungültiger Benutzername oder Passwort!"));
            delete login;
            return false;
        }

        sendRequest(requestAuth);
    }
    else
    {
        QMessageBox::critical(mParent, "THeating", tr("Sie müssen einen gültigen Benutzernamen und ein Passwort eingeben!"));
        delete login;
        return false;
    }

    delete login;
    return true;
}

This is the initialization of the dialog:

TLogin::TLogin(QWidget *parent)
    : QDialog(parent),
      ui(new Ui::TLogin)
{
    qDebug() << "DEBUG: TLogin::TLogin(QWidget *parent)";

    ui->setupUi(this);
#if defined(__EMSCRIPTEN__) || defined(Q_OS_ANDROID) || defined(Q_OS_IOS)
    // We'll center the login dialog box
    QSize psize;
    QScreen *screen = parent->screen();

    if (screen)
        psize = screen->size();
    else
        psize = parent->size();

    QRect lsize = geometry();
    int left = (psize.width() - lsize.width()) / 2;
    int top = (psize.height() - lsize.height()) / 2;
    setGeometry(left, top, lsize.width(), lsize.height());
    ui->lineEditUser->setFocusPolicy(Qt::StrongFocus);
    ui->lineEditPassword->setFocusPolicy(Qt::StrongFocus);
    ui->lineEditUser->setFocus(Qt::ActiveWindowFocusReason);
#endif
}

The 3 lines

ui->lineEditUser->setFocusPolicy(Qt::StrongFocus);
ui->lineEditPassword->setFocusPolicy(Qt::StrongFocus);
ui->lineEditUser->setFocus(Qt::ActiveWindowFocusReason);

don't change anything. Without them the behavior is the same.

Here is a screenshot of my app. You can see the frame around the top input line showing it has the focus.
On an emulator for iOS I can use the keyboard of my Mac to enter something. This works. But on a real device I have no visible keyboard.