Why is the microphone not working on my AirPods 2nd generation?

I have a pair of AirPods 2. Gen.

Now the microphones stops working from one day to another. 

They have the latest firmware 6F21.

I tried different things:

• connect to another iPhone (XS and 15) with latest iOS 18.4 -> not working
• connect to MacBook Air (2024) -> not working
• change automatic mic selection: auto, left, right -> not working
• reset the AirPods several times -> one time the mic works for 30sec in voice memo app, then stops working again -> therefore I think the hardware works and it is a software issue

Music listing/Audio works in every app. 

@Apple: It seems something goes wrong with a firmware update. Please investigate and provide a fix.

[Re-Titled by Moderator]