Why Chromium based browsers? I understand using Chrome might help Google, but how does using other browsers based on Chromium help them? By increasing market share?
Yes. It gives them leverage when working on standard specs. And it can lead to stagnation. The latter didn't happen yet, but they already tried to push their agenda multiple times already.
The only silver lining was they were also going to disable third party cookies, but they nixed that idea and kept this one. I’m done rooting for chrome.
This can be problem for Firefox and Chromium based Browsers, too. If the Website decides that Manifest v3 is mandatory to visit their site, they can block any access from Browsers with v2 running in the background easier than before.
The other 95% of all visitors will still want to see this page.
If the most visited websites use such a blocking method, then most visitors will use Chrome.