normally I'm using sound without any problems via bluetooth. Unnoticed when, the pc changed some parameters, I have no idea which and where to search. Mplayer and mpv playing as usual normal via bluetooth headphones, whereas vlc , firefox and others keep quiet. In kmix and pavucontrol bluetooth is not even recognized or mentioned, kde-systemsettings gives not hints. what should I do ? Thanks in advance wolf

I presume this is an installed system. Certainly nothing to do with using the installer or installing the system 🙂
Tag adjusted.

To be able to help, full hardware info & as many logs as possible are needed, best start with giving the SysInfo output:
https://kaosx.us/docs