Brave has integrated uBO directly into their core logic. Visit brave://settings/extensions/v2 and you can download it, even with no MV2 support. I'm not aware of any other browser adopting this approach.
firefox 149+ actually bundles brave's adblock-rust as well, it just doesn't really use it. waterfox does enable it and use it, though they're still testing (https://github.com/BrowserWorks/waterfox/issues/4182).
all of that being said, I was answering the question about mv2 broadly, not ad blocking.
all of that being said, I was answering the question about mv2 broadly, not ad blocking.