Where to start…

1. They once deployed their own cryptocurrency and used your computer to mine without consent,
2. They then manipulated all links to Amazon and some other shops to be affiliate links with themselves as beneficiary, earning commissions without user consent (and in violation of Amazon’s terms),
3. They install a VPN service without user consent,
4. They sell user data (anonymized) to train AI farms

https://www.spacebar.news/p/stop-using-brave-browser

The article is not neutral in its phrasing, but the content is correct. You’ll find other sources if you look around.