Microphone on my Apple Watch Series 5 doesn't work

I received my sister's used Apple Watch Series 5, everything is fine except that the microphone doesn't work, in fact I discovered that to make myself heard I literally have to scream into the mic hole, recording only useless noises, I have already tried to do all the steps described in the various threads on how to clean it but there is no way. asking my sister she confirmed that the mic has always worked even if she hadn't used the watch for months

[Re-Titled by Moderator]