Brave does not need manifest v2 for it's ad blocker to work. It is not implemented as an extension. It is built into the browser itself.
> We can't publish LibRedirect to the Chrome Web Store as it requires Manifest v3, which removed essential features that LibRedirect needs.
uBlock Origin is just the tip of the iceberg since it's the most popular one, there is an entire ecosystem of Mv2 extensions that can never be replaced by Brave's built in functionality
That said, uBlock Origin works best on Firefox: https://github.com/gorhill/uBlock/wiki/uBlock-Origin-works-b...
You can have all the usual ublock origin behaviour custom filter lists and all that, about:adblock