In one Channel I can hear a certain mate just with the left ear

[TS.ChrisR]

This is why.

AT2020 xlr Mic only be heard on one side

The small issue is that your Microphone tells that is a Stereo Mic but sends mono. The big problem is that the channel you are talking in has a Music codec set which is a stereo codec. These codecs are not ideal for conversations (This is why he call them Music codecs). To fix this set Opus Voice as codec and your voice is send in Mono to all channels. Or change that your device is recognized as a Stereo Microphone or let it send to both channels.

Your channel uses Opus Music and not Opus Voice as codec. This needs to be changed.