@javickers There's no need to do any Google tricks.
Just download the file for Linux from this page
https://github.com/nwjs-ffmpeg-prebuilt/nwjs-ffmpeg-prebuilt
and upload it here
/usr/lib/x86_64-linux-gnu/opera/

I need the 64-bit file, so I downloaded this one 0.101.2-linux-x64.zip

At least for Linux Mint 22.1. Then restart Opera.

This always works for me, and I do it every time I update Opera. It's a pain, unfortunately. Opera is a rather odd browser; it has some good points and a few annoying ones.