Ubuntu 20.04 Lenovo Ideapad Microphone not working

In addition to the accepted answer, check out:

• Disable PulseAudio Auto Volume

edit the following files as root:

sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-dock-mic.conf
sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-front-mic.conf
sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-headphone-mic.conf
sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-headset-mic.conf
sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-internal-mic-always.conf
sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-internal-mic.conf
sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-mic.conf
sudo emacs -nw /usr/share/pulseaudio/alsa-mixer/paths/analog-input-rear-mic.conf

And update the following fields wherever you see them in these files. You don't need to update volume if it's set to off. Only devices that are awake need to be adjusted.

• Under [Element Internal Mic Boost] set volume to zero. This includes any variations like [Element Dock Mic Boost].

• Under [Element Int Mic Boost] set volume to zero.

• Under [Element Mic Boost] set volume to zero.

Restart the computer for the changes to take effect.