I don't care about the two proprietary browsers you've mentioned, but Brave is going to (partially) support manifest v2 and maintain uBO compatibility for as long as they're able to:
Not that you really need it as Brave has its own very capable built-in ad blocker with -- last time I checked -- higher performance than uBO (since it's compiled into native code) and full support for same ad lists.
Brave is open source instead of proprietary now? I knew they were Chromium based (like the others) but I hadn't realized they switched over on all of the customizations on top.
Brave is like Firefox: it's open source, But it connects to some closed source servers to serve up contentious features (IMO this is a bigger problem on Brave than Firefox, since many of them cannot be fully hidden).
https://brave.com/blog/brave-shields-manifest-v3/
Not that you really need it as Brave has its own very capable built-in ad blocker with -- last time I checked -- higher performance than uBO (since it's compiled into native code) and full support for same ad lists.