Snapshot version of Vivaldi 1.15 has been released and allows to set a particular search engine Vivaldi ships as default in Private browsing mode.
Vivaldi by default comes with these search engines: Bing, Yahoo, StartPage, DuckDuckGo, Ecosia, Wikipedia and Google. You can set any search engine as default for regular browsing and recently released Vivaldi 1.14 allows to change their order as well, now the 1.15 version allows to set any search engine as default in Private Window.
If you’ve privacy focused you may want to set DuckDuckGo as default search engine in incognito mode, which Vivaldi team already done in this snapshot.
Vivaldi : Set Default search engine for Private browsing mode
1. Click on v icon > Tools > Settings
2. Search, select desired search engine and check ‘Set as Private Search’