Hey!
Thanks for your reply!
Yes, I downloaded the source code for Qt6.4.0 beta. Compiled it with support for "text to speech". In the new version there are more "engines" for "text to speech". And a few more features. But the speech did not get better. I suspect that the operating system's underlying capacity for speech synthesis does not work as well on Linux as on Windows.
It's just my speculations. But Qt version 5.15.5 (the latest version available as open source) gave better sound than version 5.15.2. A better and more natural pronunciation. I thought.
I need to learn more about how operating systems handle speech synthesis.