QImageCapture: setResolution works only after camera start

OSX10.15.7 with Qt6.2:

Changing the image capture resolution from default to something else only works after starting the camera but not before:

This works:

camera = new QCamera( QMediaDevices::defaultVideoInput() );
QCameraDevice cameraDevice = camera->cameraDevice();

imageCapture = new QImageCapture;

captureSession.setCamera(camera);
captureSession.setImageCapture(imageCapture);

captureSession.setVideoOutput(ui->viewfinder);
camera->start();
imageCapture->setResolution(640,480); // CALLING IT AFTER CAMERA START

This does not work:

camera = new QCamera( QMediaDevices::defaultVideoInput() );
QCameraDevice cameraDevice = camera->cameraDevice();

imageCapture = new QImageCapture;

imageCapture->setResolution(640,480); // CALLING IT BEFORE CAMERA START

captureSession.setCamera(camera);
captureSession.setImageCapture(imageCapture);

captureSession.setVideoOutput(ui->viewfinder);
camera->start();