Headset microphone not working on Ubuntu 20.04

When I'm speaking with my internal microphone and I connect my headset, it's not detecting the microphone on it. Thing that does not happen in Windows, also didn't happen in Ubuntu 18.04

Any suggestion to fix it?

So, trying various stuff I am not sure which step was effective. Ubuntu 20.0.4 using Cinnamon (no Gnome/KDE) on Dell XPS 9340:

1. rm -rf ~/.config/pulse/
2. Log out
3. Log back in
4. go to desktop settings/'sound'
5. insert headphones
6. Go to 'input' section
7. Do microphone audio test on each available device

Headphones start working...

So after having this issue with beautiful, but already annoying, 20.04, I found a solution in another post at SuperUser. In my case what helped me was:

1. Use the following command to get the Audio Codec for your machine's model:

   cat /proc/asound/card*/codec* | grep Codec
   

   In my case I saw the following audio and video codecs:

   Codec: Realtek ALC233
   Codec: Nvidia GPU 94 HDMI/DP
   

2. Go to www.kernel.org, look up the version of the codec, and get the full name of it. In my case, for Realtek ALC233 it's alc233-eapd.

3. Create/update the /etc/modprobe.d/alsa-base.conf file, and add this line, replacing the model with your own:

   options snd-hda-intel model=alc233-eapd
   

4. Reboot the machine.

What fixed this for me was running pulseaudio -k in Terminal.