Question: Why don't I hear the audio from my computer on my MacOS recording?
Answer: If you don't here the audio from your computer on your MacOS recording, it's likely you were making a Full Screen recording rather than a Browser Tab recording.
NOTE
If a recording does not have the desired audio, the audio cannot be recovered.
Due to system limitations imposed by Apple, it's impossible to record system audio on Macs (the sound coming from your computer during a full screen recording).
To record the sound coming from your computer on a Mac you will need to make a "Browser Tab" recording.