With the reference to the old post from 19 December 2019, sound events don't work in Solus Mate by default. Even though required canberra packages are installed, canberra-aware sound themes are present, sound-related DConf settings are enabled.
The reason is missing GTK_MODULES environment variable. Defining and setting GTK_MODULES in the /usr/share/defaults/etc/environment file seems to be an acceptable solution:
GTK_MODULES=canberra-gtk-module
All sound events start to work fine. Solus Mate is not as mute as a fish now.
The issue is solved.
