Although Opera allows you to use custom search engines by setting a keyword before your query, it does not currently allow you to set your default search engine to anything except six choices. This is a great start—for privacy-conscious users, DuckDuckGo is one of the options, and I've been happy to use it.
However, there have been 70 threads in the Opera forums talking about another search engine—Ecosia—which uses the profits it earns from ads to plant trees. In a 2016 article, it was estimated that Google receives 63,000 searches per second. I'm willing to bet that number is even higher now, but if that many searches were done using Ecosia, that would result in around 1,400 trees planted (63,000/45 searches per tree).
This is a significant way that people can contribute to environmental causes without major commitments, or even investments of time. However, it is only effective if users can do it conveniently.
By enabling Ecosia as one of the default search engines available for users to select, that would raise awareness of it and result in a more sustainable internet. Barring that, even enabling custom default search engines would allow people to switch over to this search engine without the inconvenience of typing a keyword before their search. This may seem minor, but convenience can dramatically impact people's choices in how they search.
Please add Ecosia as a default search engine available for selection, or allow users to choose custom search engines to be their default. I've been happy using Opera for the past two years, because I believe in its values—the internet, open standards, and people. Ecosia supports those same themes, and I would like to use both without having to find workarounds, extra clicks, or extra keystrokes.