I'm not sure if this will help for all, but its worth a shot.
I've had the same audio issue for a bit, after my computer blue-screened and had to reset. I had cleared out my %temp% files, and I had manually ended the process on Task Manager. If you scroll down on TM, there should be one that says "Opera GX Browser". I ended the process, opened up OGX again, and noticed the sound had returned.
Like I said, this may not work for all, but it is worth a shot. Apologies if this does not work, I am not specialized in this type of stuff.