I use firefox so i don't know much about chrome vs chromium politics, but if the chromium people have one thing to do now, it would be to maintain manifest v2 in their fork..
Unless something recently changed, Chromium is considered upstream for Google Chrome, not a fork... so you will see most engine level changes originate in Chromium, by google engineers.
Maybe you are confusing it with de-googled-chromium et al?
chromium people are chrome people. google provide chromium either as a literal requirement for compliance with some other open source licence, or as a vestige from the “don’t be evil” days.
Maybe you are confusing it with de-googled-chromium et al?