Do you have any information on how the actual patent licensing is set up for Vivaldi? I wasn't able to find much on it, though I see the note in https://wiki.archlinux.org/title/Vivaldi that it “automatically downloads” the relevant files, which is at least suggestive that they can't just redistribute the binaries normally. The other closest thing I was able to find was https://github.com/chromiumembedded/cef/issues/3559 which describes a specific proprietary_codecs option in CEF, which is not quite the same thing but ought in some sense to be related… the way they describe having to set ffmpeg_brand=Chrome normally for that to be available doesn't sound promising?

I would be moderately surprised if whatever arrangement is going on there allows full use of the codecs for video editing software and not just for consumer decode of Web resources.