Hi, my comment in https://blogs.opera.com/desktop/2020/12/opera-73-0-3856-235-beta-update still applies to opera 73.0.3856.329 and opera-beta 74.0.3911.22 (Ubuntu Linux x64 versions)
I can't play the video e.g. on https://www.facebook.com/extra3/videos/865783870855977
Solution:

roland@hp:~$ cd /usr/lib/x86_64-linux-gnu/opera-beta/
roland@hp:/usr/lib/x86_64-linux-gnu/opera-beta$ sudo mv libffmpeg.so libffmpeg.so_orig 
roland@hp:/usr/lib/x86_64-linux-gnu/opera-beta$ sudo ln -s /usr/share/code/libffmpeg.so .
roland@hp:/usr/lib/x86_64-linux-gnu/opera-beta$ cd ../opera
roland@hp:/usr/lib/x86_64-linux-gnu/opera$ sudo mv libffmpeg.so libffmpeg.so_orig 
roland@hp:/usr/lib/x86_64-linux-gnu/opera$ sudo ln -s /usr/share/code/libffmpeg.so .

Please provide a recent libffmpeg.so as distributed with MS Visual Studio Code, Chromium snap or skypeforlinux.
Thank you!

roland@hp:~$ locate libffmpeg.so|xargs ls -l
-rwxr-xr-x 1 root root 3445640 Dez  3 22:20 /snap/chromium/1424/usr/lib/chromium-browser/libffmpeg.so
lrwxrwxrwx 1 root root      28 Jan 13 17:10 /usr/lib/x86_64-linux-gnu/opera-beta/libffmpeg.so -> /usr/share/code/libffmpeg.so
-rw-r--r-- 1 root root 1836280 Jan  5 23:17 /usr/lib/x86_64-linux-gnu/opera-beta/libffmpeg.so_orig
lrwxrwxrwx 1 root root      28 Jan 13 17:12 /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so -> /usr/share/code/libffmpeg.so
-rw-r--r-- 1 root root 1835752 Jan  5 09:02 /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so_orig
-rwxr-xr-x 1 root root 2855920 Apr  1  2020 /usr/share/code/libffmpeg.so
-rwxr-xr-x 1 root root 2962992 Nov 19 12:57 /usr/share/skypeforlinux/libffmpeg.so

Hi, for a long time I have been unable to play embedded videos on facebook with th newest versions of Opera Beta on Ubuntu Linux, e.g. https://www.facebook.com/bosettisarah/posts/4094659607229685 .
The same videos played fine on Google Chrome.
Now I found https://forum.ubuntuusers.de/topic/opera-spielt-keine-facebook-videos
After

roland@hp:~$ locate libffmpeg.so|xargs ls -l
-rwxr-xr-x 1 root root 3456432 Nov 18 13:06 /snap/chromium/1411/usr/lib/chromium-browser/libffmpeg.so
-rwxr-xr-x 1 root root 3445640 Dez  3 22:20 /snap/chromium/1424/usr/lib/chromium-browser/libffmpeg.so
-rw-r--r-- 1 root root 1835752 Dez  1 22:43 /usr/lib/x86_64-linux-gnu/opera-beta/libffmpeg.so
-rw-r--r-- 1 root root 1835752 Dez  7 22:54 /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so
-rwxr-xr-x 1 root root 2855920 Apr  1  2020 /usr/share/code/libffmpeg.so
-rwxr-xr-x 1 root root 2962992 Nov 19 12:57 /usr/share/skypeforlinux/libffmpeg.so
roland@hp:~$ cd /usr/lib/x86_64-linux-gnu/opera-beta/
roland@hp:/usr/lib/x86_64-linux-gnu/opera-beta$ sudo mv libffmpeg.so libffmpeg.so_orig
roland@hp:/usr/lib/x86_64-linux-gnu/opera-beta$ sudo ln -s /usr/share/code/libffmpeg.so .

It works fine now.
Please consider to upgrade the included libffmpeg.so on Linux.