The issue for me, running openSUSE Leap Release 15.4 64-bit, is that the available and installed chromium-ffmpeg-extra version is: 103.0.5060.114-150400.2.pm.1
The latest Opera version 100.0.4815.13-0, is using Chromium version 114.0.5735.133 and as such the mismatch to the to elements prevents video from playing in Facebook and other web pages.
I acquired the chromium_114.0.5735.133 package and extracted the version 114.0.5735.133 libffmpeg.so, but it requires updated package:
opera: /lib64/libm.so.6: version GLIBC_2.35' not found (required by /usr/lib64/opera/lib_extra/libffmpeg.so) opera: /usr/local/lib64/libc.so.6: version GLIBC_2.34' not found (required by /usr/lib64/opera/lib_extra/libffmpeg.so)
which is not available for my distro as yet it seems.
I reverted Opera back to the distro supplied 99.0.4788.13-lp154.2.47.1 with the original libffmpeg.so, and video plays as before.