I don’t check the source code of something big browsers, that’s a little beyond my understanding, but that’s why there are experts for that.

The webrequest api (or rather the main parts) have already been phased out of chromium, so it’s just a matter of time until Vivaldi rebases to the newest version and gets rid of the api. (I think they said they want to delay the depreciation but acknowledged that it is inevitably coming, probably sooner than later)