In built microphone works on Linux only if I have headphones plugged in

I have read in the community that there are problems with the V hardware on Linux. I have observed a strange behaviour and I think it might be fixable, so I would like to get advice if you have any.
The behaviour itself: The inbuilt microphone doesn’t work on Ubuntu 18.04 or 20.04., except if I plug in headphones in the headphone jack. Note that I tested this with headphones that have no mic (Philips SHE2000) and I also performed a check with the Ubuntu sound settings, that showed the sound input source is located at the top of the screen, not it the headphones.
So, how can I make the inbuilt microphone work even if I don’t plug in headphones? Thanks