Here is a list of things you can do to troubleshoot why your audio recordings are not playing in OneNote for Mac:

1. Check that the QuickTime Player is up to date and installed on your Mac.
2. Ensure that OneNote has the appropriate permissions allowing it to control QuickTime Player.
3. Try playing the audio recordings on other media players such as Windows Media Player and RealPlayer.
4. Check audio file compatibility. OneNote only supports a limited number of audio file formats.
5. Test the same file on another Mac. If it plays, then the issue could be related to your Mac.