Brave is run by a VC-funded company and will need to show returns eventually. To date, they've tried to make money in a few disappointing ways:

- Replacing ads on pages without owner's intervention, under the guise that they were offering owners a cryptocurrency

- Inserting their own referral codes on websites

- Installing their VPN software on Windows machines without consent

They also introduced a Tor mode into their browser that sent DNS requests unmasked to your ISP. I don't know why you would trust Brave at this point.