Most likely: You will become their product that’s it and be sold as part of their audience and then crypto-bros can invest on you watching their ads + have your local browsing history analyzed + your searches spied by their search engine (but it won’t be Google they promise, and they will keep their promise).

At the origin, Brave was supposed to be an adware that replaces the ads of the website with theirs.

Just pick your poison but all browser developers need money to live.

The only way to be sure a browser works in your best interest would be if you accept to pay, and nobody wants to do that.