Do Chromium-based browsers also adopt this Manifestv3? If so, isn't Brave Chromium-based?

No they don’t, they manually merge code from upstream if they like it. Since Brave doesnt like it they wont merge it.

If Google makes enough changes that eventually makes it impossible to merge upstream code while maintaining compatibility with the old APIs, then Brave and everyone else will either be stuck with old and unpatched Chromium versions or they'll have to waste resources to keep things working.

Not everyone has the resources to maintain their own Chromium fork and it's not easy to keep up with Google, Microsoft, Samsung, etc. Just look at Firefox.

They already de-google the entire codebase. You can see which parts are removed here https://github.com/brave/brave-browser/wiki/Deviations-from-... and they keep up quite well.

Yeah... what happens when Google decides something important can't work without one of the disabled features?

Look, Google controls Chromium and they have the resources (and incentive?) to keep these smaller browsers running in order to keep up with them.

That's not actually true. Brave's system uses a Chromium commit hash as a base, then applies patches on top of that. They'll have to manually move the old API implementation into patches and continue to maintain it there.

Source: I've collaborated with / worked on Brave in the past.

Sounds like they need a more comprehensive response with this move

Won't this create a problem for them when it comes to the extension store since no new v2 extensions will be able to be deployed there even though other chromium based browsers support them?

Firefox will move to v3 while retaining the old webrequest APIs, so there will extensions around that would work.

Are you being serious?

https://gs.statcounter.com/browser-market-share

It was a snub at Chrome. I understand that the vast majority of the world uses Chrome, I just think it's foolish if you want to preserve your privacy.

Chrome has been anti-user, anti-usability for some years now.I don't even want to recall the disgusting changes they did that made it unusable for me,among: website-wide audio mute, disabled click-to-mute audio.

Frankly do you consider market share a legitimate argument?It's not,and the fact that some 'tech-literate' people still use chrome baffles me.Same goes for Firefox, but my problems with them are not so much about their browser/tech but other which are not pertinent.