MacOS – Earbud Audio Not Working

Take a look at this Apple Support article. Not exactly your problem, but similar.

Basically, it says that it there's nothing clogging the audio-related components. If there is, it suggests cleaning them and tells you how:

If the speaker, microphone mesh, or top microphone (iPhone 4 only) appear clogged, please use a clean, small, dry, soft-bristled brush to clean them. To do this follow these instructions: Use the brush to carefully and gently brush the speaker and microphone mesh. Brush away from the 30-pin dock connector to avoid getting any debris into the dock connector.

And, if that doesn't work, Apple suggests that you get it serviced.

The red light in your audio out jack indicates that it is active. That is why you do not hear anything on the speakers.

Your analog/digital switch in the port is stuck -- the red light is the digital audio signal.

Try to plug the headphone in, this time wiggling it from side to side while it's plugged in.

Alternatively try cleaning the audio plug:

Try inserting a cocktail stirrer or a toothpick and jiggle it around in the audio output port and the internal speakers should come to life.

If you have a compressed air can use it. that seems to work best.

There is a switch inside that has to be tripped.