Vivaldi opens a link only if there is a running instance of vivaldi.
Version: 126.96.36.199 (Developer Build) preview if you click on a link and vivaldi is not running, the browser starts but the link won't open. So you have to click on the link again to make vivaldi open the link. But if there is a running instance of vivaldi, then it will open the link (as expected).
Vivaldi 188.8.131.52 (Developer Build) snapshot
This version fixes the bug even though the changelog doesn't mention it.