Took 2 seconds to startpage* this: https://vivaldi.com/blog/vivaldi-business-model/

*screw Google and their AI search

Search engine deals are HUGE for browsers. They're e.g. what has funded Mozilla with many billions over the last 20 years. Mozilla has tried to diversify but everything else has pales in comparison (and the donations are basically a joke).

It scales up with usage as well. Not that Safari needed funding, but Google pays Apple upwards of $20,000,000,000 per year for the privilege of being the default for that user base.