I had the same problem and it turned out to be a recording app I was using called Loom. As soon as the free version ran out and it went to the free version I had no audio on Zoom even using a headset. Happened on my husbands laptop too after I installed Loom on there. I had to dial into my Zoom meetings by phone!
As soon as I uninstalled the app we had audio on both laptops.
So it could be a recording or similar app interfering with your audio.