(Brave employee here)

The Rewards feature of Brave is what allows users to pay creators and also opt-into ads. This feature is completely optional though. It's off by default and users never get bothered about it

Brave is actually a proper fork of the Chromium code-base and builds on top of it, which is a lot more involved than a theme. The work that's been done is fairly significant if you wanted to give it a try. Even if you never enable Rewards, there are some great features and under-the-hood tweaks for privacy, Ad-blocking, and tracking protection

There's a list of ways that Brave deviates from Chromium here for quick comparison: https://github.com/brave/brave-browser/wiki/Deviations-from-...