$ dpkg -l |grep opera
opera-beta 71.0.3770.126 amd64
opera-stable 71.0.3770.148 amd64
$ cat /etc/lsb-release
DISTRIB_DESCRIPTION="Ubuntu 20.04.1 LTS"

Multiple try, no sound on FB video.
Same on beta and stable version, but the same FB video have sound on Firefox.
Youtube on Opera works with sound.

Any Idea ?

Many thanks !