audio output format automatically switches to 1 ch when I call using slack/zoom call

I use bluetooth earphones/ headphone, normally the format in MIDI is 2 ch ...., but whenever I call using slack or zoom the format automatically switches to 1 ch ....

The sound quality degrades for the whole system and also I can't change it back to 2ch.

As soon as I end the call the 2ch is automatically selected.

BEFORE CALL (NORMAL):

DURING CALL:

AFTER CALL: