I installed xbindkeys and edited /home/user/.xbindkeysrc.
To create a default condfiguration file, type: xbindkeys --default > /home/user/.xbindkeysrc ## Volume down "mixerctl outputs.master=-5" m:0x0 + c:122 XF86AudioLowerVolume ## Volume up "mixerctl outputs.master=+5" m:0x0 + c:123 XF86AudioRaiseVolume Now the keyboard controls for sound work.