One AirPod not working.

Maybe this? --> How to clean your AirPods and EarPods - https://support.apple.com/HT208729

also:

Click on this link to learn how to 'Reset your AirPods --> https://support.apple.com/HT209463

Click on this link to learn 'How to reset your AirPods Max '--> https://support.apple.com/HT211904

If you need more help Contact - Official Apple Support

Click here --> https://support.apple.com/contact

or

'See a list of Apple phone numbers around the world'

Click here --> https://support.apple.com/HT201232

I have the exactly same situation, left AirPod is considerably quieter than the right one. Called Apple and follow all the advices, cleaned then restore to factory settings, un paired and paired again, nothing. Tried with another device, which I did with my Ipad. I am very careful with this expensive devices, no water, no drop it. The only response from Apple is that because is out of warranty I need to purchase a replacement and cost $ 70. Completely disappointed.