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.