I’ve looked at suggestions on StackExchange and made some changes to files in /etc but after each login or reboot it is up to 100 % again in pavucontrol. On this computer I hardly ever use the speakers, and I want the microphone muted, always, so I guess I could even block list a few kernel modules for sound (which ones ?). But why can a desktop user not easily turn volume to zero, forever ?
Edit : Thanks all. It was not StackExchange but on AskUbuntu from where I tried some suggestions. I also tried muting audio in Pavucontrol but that didn’t help between logouts and logins. Now I have set the default audio device in Pavucontrol to Dummy, and that works. I can still play sound from a video in VLC, but the microphone keeps muted.
I think this should work (I haven’t tested it):
make a new file called default (.) pa in the pulseaudio congfig folder (.config/pulse)
this will mute source_name (replace source_name with your source name):
#include this config file .include /etc/pulse/default.pa set-source-mute source_name true
run this command to list source names:
pactl list short sources