Call Quality - Can't hear the caller or they can't hear me!
In most cases, calls are routed to your main cell phone number, therefore, your provider handles the quality of the call. However, generally deleting and reinstalling the app will resolve this issue.
If you are using In-App Calling (VoIP) or use the Sign in with Google/Apple method, call quality is determined by your signal strength and connection. You can try disabling that feature, deleting and reinstalling the app or both! One of the 2 options generally fixes this issue.
Note: If you are a Sign in with Google/Apple user, you do not have the option to turn off In-App Calling (VoIP). Therefore, it's best to delete and reinstall the app.