Edit: guys I know that Brave is not the best browser and I wouldn't recommend it, but I haven't seen studies or in depth articles about technical details of privacy concerns.
And I'm not being sarcastic, I wanna see them so I can make a more informed opinion.
This isn't really a "privacy concern" from a user standpoint.
It isn't user data they're selling, it's data they've scraped from websites for use in machine learning. It's more of a legal grey area in the same way that OpenAI is being sued for their use of data in training ChatGPT.
The main point people need to understand is that Chromium based browsers are heavily nerfing the ability for users to use ad-blockers. This isn't much of an issue in the case of Brave where the ad-blocking is built into the browser itself.
And personally, I would rather have some healthy privacy based competition between browsers. Having both Librewolf (Firefox) and Brave browser (chromium) lets us have options to switch between.
It also creates additional work on the advertising side in this cat and mouse game.