I've just upgraded my Ubuntu from 18.04 to 20.04.
I've noticed that when I increase or decrease the volume, I no longer hear a notification sound, which was very useful for me.
As a funny side effect, now I do hear a notification sound whenever I increase or decrease the microphone volume, that wasn't the case before and I find it nice.
How can I enable the sound of volume-up and volume-down events again?