Not just the right mouse button, but the keyboard modifier keys as well would be nice.
Back when I was still using Firefox, I got accustomed to the option buried under about:config that let me set a different scroll distance for the mouse wheel based on which modifier keys I hold down.
The closest I found in Vivaldi was the "Chrome Wheel" extension, which doesn't work in Vivaldi anymore (though it does in Chromium). That one just gives you a single fixed scroll distance with any modifier key, though, not a configurable amount.