"Unknown Audio Device"

Every time I plug in my headphones, Ubuntu shows a popup box asking whether I've plugged in headphones, a headset, or a microphone.

How do I get it to stop doing this?

I have the same pop-up in Ubuntu 16.04, whenever I plug in my headphones:

Apparently, there was an option to disable it in the previous versions, mainly because of the changing hardware for headsets. Previously, there used to be different jacks for speakers and microphones, but today's machines have merged them into one. Different standards too cause problems in autodetection.

Have a read here: http://voices.canonical.com/david.henningsson/2014/03/07/headset-jacks-on-newer-laptops/

You can lie to Alsa by appending

options snd-hda-intel model=headset-mic

onto the end of /etc/modprobe.d/alsa-base.conf, followed by a reboot.

This works for XPS15 under Ubuntu 19.04 and 19.10 but it should also work for any Intel-based audio card.