I've had this issue with Ubuntu starting from 16.04 and it still persists in Ubuntu 20.04.
Here's the problem: whenever I plug in my headphones, it asks me to select an audio device (it gives me three options: headphones, headset and microphone), and even if I don't select one and click Esc
, the headphones still work, so that tells me this prompt might not be necessary but I couldn't find any way to disable it.