A new default: Private Search
The Private Search setting is a default search exclusively for Private Window browsing. The latest version of Vivaldi adds a more private default search experience to the Private Window by utilizing DuckDuckGo by default.
To change your default Private Search, open a new Private Window from the File menu and use the dropdown menu on the welcome screen to select one. Or, navigate to the Search Settings and tick 'Set as Private Search' next to the engine you'd like to use.