Chromium version 78.0.3904.108 is provided with Mageia 7, and sound is broken in this version.
Some searching reveals that the problem is due to the chromium sandboxing policy. It seems that it is too tight and as a result sound can't be made to work.
The workaround is to start it from the command line as: "chromium-browser --no-sandbox". Sound then works, though apparently there are security implications.
I do hope that gets fixed soon.