Earlier quoted context omitted.
Do you happen to know how they make money, or can maintain the project going forward? Seems they don't charge for their browser, and also claim they don't monetize their user's personal information at all.
They get paid to set the default search engine to Google.
Vivaldi generates revenue from partner deals with search engines. Every time you search using one of the pre-installed search engines, you’re helping us grow, one search at a time. Currently, we work with DuckDuckGo, Ecosia, Startpage, Yahoo!, Bing, and Yandex. The only exception is Google – we don’t make money when you search with Google. However, we know that some of you use this search engine daily, so we include it in Vivaldi.
(Source: https://vivaldi.com/blog/vivaldi-business-model/)
The other other source of revenue is bundled partner bookmarks (see again the linked document).