Adless monetization is a very difficult challenge - something I've worked on many times over the years (compute-monetization, shopping-commission monetization, payment interchange monetization) and it's always been very difficult to compete with ads. I think the waterfox approach of "ads if you're OK with it" opt-in and sane defaults is the better one, but it's very difficult to make ends meat compared to competitors offering full monetization on by default when you're only getting it (and getting less per search) if users opt-in.

Compute/resource monetization is the one after all these years that has done the best at replacing ads as a means of monetization for users, and it requires a very intelligent scheduling system + ethical ecosystem to work (most have just tried running crypto miners that cost users more electricity than they earn).