Invalid preferredFormat is returned for iMac's built-in audio device, see
Environment section for full device specification.

It seems doesn't depend on macOS version, reproduced on macOS 13.7.8 and 14.8.1 (tested on 2 machines with the same HW)

I.e. it triggers an assertion in the next code, and any related functionality, e.g. QAudioSource::start() also does not work, when using a built-in device.

    const auto device = QMediaDevices::defaultAudioInput();
    const auto format = device.preferredFormat();
    Q_ASSERT(format.isValid());

After some debugging, it was discovered that the root cause for the problem is that the sampleFormat parameter has the Unknown value for some reason.

So, "preferred" format looks like:

sampleRate = 44100, sampleFormat = Unknown, channelCount = 2