I think Jon said somewhere that to start being profitable they needed something about 3 million users, and Vivaldi already has more than 800 000 according to their page and I heard some other sites saying it's already at over 1 million.

That's surprisingly economical, much more than I expected. I suppose "no tracking" search engines like DDG have a similar approach.

Actually I don't thinks it's so surprising, the 90s did not have tracking and companies have survived and grown.

But tracking is probably +5x more profitable minimum, while Vivaldi or Mozilla might get some $1/user Google probably makes $5-$15/user. And the reason of all the tracking and why companies fight so hard against legislation that try to cut their cash cow.

Are there any "open" ad-targeting platforms, where you get to see where and how your data is used?