AirPods Gen 1 microphone sounds muffled the first seconds while talking

Hello, I got my AirPods Gen 1 for about 5 years now and have only used them for about 1.5 or 2 years because at one day the microphone sounded muffled when I was on the phone with someone. I did all the steps you can find on the internet like resetting them, reconnecting them, disconnecting from all other bluetooth devices, cleaning them carefully, changing the microphone from left to right and also automatically. So basically every tutorial you can find on the internet.

Today I tried to use them again, because it would be a waste if they just lay in my drawer not being used.

I now found out that the sound is only muffled the first seconds while talking. So if you are talking without taking a break, the sound suddenly is crisp and clear and if you continue talking the sound even stays clear. But when you then stop talking and take a 5 second break and try to talk again, the sound is muffled again for the first few seconds.

So technically the hardware of the microphone should be in good condition, but somehow the software muffles the sound the first few seconds and only makes it crisp and clear after a few seconds of talking.

In other communities you can also see that many others are having the problem of muffled microphone sound who can not get it fixed. So is there anyone who knows how to fix this kind of software problem? I know that a software downgrade is not possible for whatever reason...

I would like to use these AirPods again or gift them to someone out of the family but first they need to work again.

Thank you in advance.