How do I improve audio quality when calling with 3rd party apps? (e.g. Messenger, Discord, Zoom, etc.)
Facebook messenger, Google Duo and other messaging app call use internet connection. Many internet service provider restrict bandwidth for such call. Using 5G network can improve your call quality.
You can use Lease line for internet connection. Such connection does not have any speed limit. You need Lease line on both side then you can get good call quality.
Also update your app to latest version.