My left AirPod is very quiet. I’ve tried all the obvious (reset, audio balance etc) but it hasn’t fixed

Hello ~ Have you checked to see if they need cleaning? Take a look here…

How to clean your AirPods, AirPods Pro, AirPods Max, and EarPods - Apple Support

The screen may need clearing of debris.

~Katana-San~

Hello ~ Well… you have done everything else that I myself would try. You may just need to go ahead and have them checked out…

AirPods Repair & Service - Apple Support

Genius Bar Reservation and Apple Support Options - Apple

I wish that I could be of more help.

~Katana-San~

Hello again ~ You are welcome. Good luck:)

~Katana-San~