Allow desktop app to access your microphone if you launch PowerPoint directly from your desktop app.In the left-hand pane, scroll down to App permissions → click on Microphone.Otherwise, apps won’t be able to record audio or video input.
Users need to specifically confirm what apps can access their camera or microphone. Microsoft has taken privacy very seriously in Windows 10. ⇒ Note: Just in case, check your microphone volume and make sure your mic is not muted. Fix PowerPoint Audio Recording Issues on Windows 10
