External earphone mic stopped working

Microphone stopped working for external earphone. The earphone itself works, I can hear sounds well, the problem is only with the mic. I would like to use it again.

I already checked a few related posts, for example:
- https://askubuntu.com/questions/1138408/mic-device-not-working-on-ubuntu-18-04
- https://askubuntu.com/questions/1112445/18-04-1-lts-mic-not-working
- https://wiki.ubuntu.com/Audio/CheckForMutedMicrophone

Currently, I am going through the steps of this guide:
https://help.ubuntu.com/community/SoundTroubleshootingProcedure

For a starter, there are some screens of settings:
- Audio settings: https://imgur.com/a/xYP9LWL
- Pulseaudio: https://imgur.com/a/PO1jDB7
- AlsaMixer: https://imgur.com/a/jP61dDk

What they show:
- 'Settings' does not recognize the microphone
- 'Pulseaudio' recognizes an external microphone but sees no input. There, the mic is not muted. The channels are locked and whenever I unlock them they become locked again after a system reboot.
- Alsamixer shows that the microphone is muted and volume is on zero. I can unmute it and pull up the volume but that does not make it work and then becomes reset after a system reboot.

alsa-info output: https://pastebin.com/iNnN16FC
diagnostics output: https://pastebin.com/1xLRULEL

Specs:
- Dell Latitude E6400
- Ubuntu 18.04.2 LTS

I would appreciate any guidance. Thanks!