As long as websites/advertisers see their visitors as using a Chromium based browser they will continue to target for Chromium, regardless of whatever front facing UI is used.
The inherent problem is Google has an outsized voice in Chromium’s developmental trajectory, and any major changes to Chromium will have downstream impacts, whether in actual implemented feature sets or forks making continued modifications on top.
The best way to protest is to not use a Chromium browser. Switching from Chrome to another Chromium browser is at best a side grade; everyone using Chromium is subject to Google’s whimsy.
Pragmatically it doesn’t matter if Microsoft chooses not to implement it; as long as Edge is on Chromium, Google can leverage this to continue to bully the web to their own devices.
Google gained control of the web by populating the world with Chrome/Chromium and wants to strong arm the web as a whole through it. Climbing the ladder and pulling it up from underneath them, with their fisted approach to Manifest V3 the beginning salvo.
For Google it’s just another day in the office.