Vivaldi is the only browser I know, that doesn’t allow you to tab to links on websites by default. It’s a very odd decision in my opinion and it baffled me again today, since I recently switched to Vivaldi on my work machine too.

So that I (or you) don’t struggle with this again, here is how to fix it:

1. open Vivaldi’s settings
2. search for "Webpage Focus"
3. make sure "Focus All Controls And Links" is activated

Then you should be able to properly test keyboard focus on websites like you can in all other browsers.