This may be related to the issue observed in https://bugreports.qt.io/browse/QTBUG-98100.

In a code snippet on https://doc.qt.io/qt-6/qmediaplayer.html, there's a code snippet under "Detailed Description" that includes the line
audioOutput->setVolume(50);
This does not work since QAudioOutput::setVolume() will expect a float argument between 0.0 and 1.0, not an integer.

This is purely a documentation bug, the code snippet works fine if the "50" is replaced by "0.5".