There is no pure browser anymore. The little red hen of Google funds everything, and forks like Waterfox just change a few parts of the UI but still rely on the upstream for all actual browser code. Even Mozilla was bootstrapped by AOL-Time Warner Back in the day. If you look at Ladybird they already have lots of ad companies funding it as well and will demand its enshittification if it gets popular.
Have you checked out Ladybird, it's independent.
Which of Ladybird's sponsors are adtech? None of their websites proclaim them to be in the advertising business at least.