music issue with dance class with MAC

I use zoom for dance classes since the covid and everything worked just fine. I recently change my computer, but still on MAC, and I tried for hours to change the settings and it seems that the sound does not comes directly from the computer because we can hardly hear anything while my voice with the external mike works just fine... I had to cancel a class and may cancel another one if I don't find the solution. HEEEELPPP please!!!