try replacing opera's libffmpeg.so file with the one chrome uses, this is a linux fix, not tried it for windows
https://gist.github.com/Thomas-Ln/c4ae803e90f9984b6612c8983c8fde1f

@stevejones

Re: Youtube videos not working in Opera

I've found that in Linux Mint, Opera has difficulties playing videos from a number of sources.

If you copy the libffmpeg.so file from /lib/chromium to /lib/x86_64-linux-gnu/opera (replacing the one that's there), videos will spin up and play from any (so far) tested source.

try replacing opera's libffmpeg.so file with the one chrome uses, this is a linux fix, not tried it for windows
https://gist.github.com/Thomas-Ln/c4ae803e90f9984b6612c8983c8fde1f