I unable to do audio recording in Kdenlive. Audio device does not show in Settings => Configure Kdenlive => Capture => Audio tab.
To fix this issue, install libqt5multimedia5-plugins.
$ sudo apt install libqt5multimedia5-plugins
Restart Kdenlive and go to Settings => Configure Kdenlive => Capture => Audio tab. Audio device list will be shown and audio recording can be used again.