Based on your description, I suspect this is an Android WebView limitation rather than a Mendix issue.
Most voice recording features rely on the standard Web API getUserMedia(). While this works in Chrome and other browsers, it may not behave the same way inside the Mendix Native WebView, even if microphone permissions are already granted.
Instead of relying on the WebView to access the microphone, I would recommend using the Native app itself to capture the audio:
This approach avoids depending on WebView support for getUserMedia() and is generally more reliable for Native applications.
Before proceeding, I would also verify whether the external voice library officially supports running inside Android WebView. If it only supports Chrome/Edge browsers, that would explain why it works everywhere except inside the Mendix Native app.
Kindly mark this as the accepted answer if it helps.