I'm having the same problem and have had it for a while.
Version:
You have Microsoft Teams Version 1.4.00.13653 (64-bit).
OS
$ uname -a
Linux ---- 5.11.0-31-generic #33-Ubuntu SMP Wed Aug 11 13:19:04 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 21.04
Release: 21.04
Codename: hirsute
One user mentioned restarting Teams. You can easily do that using the icon by the clock. Closing the Teams window may leave it running in the background, but if choose "Quit" from the menu by the clock, it will fully close it. I've had lots of screen artifacts and crashing issues after suspend even without the sound issues, so it's gotten to be a normal thing for me.
I also noticed Teams doesn't like changing the sound inputs. When I plug my laptop into my dock, it sees the new input right away for some reason. But, when I connected my bluetooth headset it wouldn't see it. I could set my system to use the headset and tell Teams to use the default system device. It would ring in my headset and then switch to the main speakers for the call. Crazy! When I closed and reopened Teams while the headset was already connected, the headset was in the device list in Teams settings, and it worked great.
I have also found that doing a test call seems to fix the sound somehow. It's annoying ,but I've gotten in the habit of doing a test call to check the sound before every call. I think that fixes things as much as it checks them.
I'm thinking about trying to configure a loopback sound device to see if I can pipe things to that device and just have teams restricted to that device. I'll comment back if I can get that working.