Look: https://doc.qt.io/qt-5.10/qtexttospeech.html#volume-prop at volume property is defined as double, but notifier signal is declared as
Simple way to workaround is connect this signal to some slot like: void function(int) and in this slot get current volume value from QTextToSpeech object (you have got access to it in this case).
|For Gerrit Dashboard: QTBUG-66209|
|223142,15||Fix type for volume in property: double instead of int||5.11||qt/qtspeech||Status: MERGED||+2||0|
|232869,2||Extend blacklisting of volume test to cover openSUSE 15.0 as well||dev||qt/qtspeech||Status: MERGED||+2||0|