Since around today, March 10, 2021 and recent update to 89.0.4389.82 Chromium stopped syncing to Google accounts. This is due to some changes by google
What should we do as users?
There's literally nothing that can be done by users or anyone other than Google to change this. You will need to use the actual google chrome browser if you want to use profile synchronization
Google made the decision that their profile sync apis are going to be restricted to google chrome only, and it's a decision by google, not by chromium or users of chromium, that we can't alter. Their announcement on that change even said march was the date that this would get yanked, and march 15 would get actual login failure cases.
This is stated perfectly in the comment you linked to in that 'bug' (all 'bold' emphasis is mine).
This is an unfortunate consequence of a decision by Google to restrict access to the sync API to Chrome only (which explains why in comment #3 you're seeing that chrome 89 on linux works fine).
And the quote by the ubuntu developer from the chromium upstream site data.
« What does this mean for my users?
Users of products that are incorrectly using these APIs will notice that they won't be able to log into their Google Accounts in those products anymore.
For users who accessed Google features (like Chrome Sync) through a 3rd-party Chromium-based browser, their data will continue to be available in their Google Account, and data that they have stored locally will continue to be available locally.
And yet again the developer makes a statement
I'm afraid (and sorry) there's nothing that can be done from a packaging perspective to mitigate this regression. Reverting the snap in the stable channel wouldn't help, because it's not a version problem. The official announcement states that starting March 15 attempts to log in will fail anyway.
I suppose that users that can't do without the profile sync feature will need to move on to using the official chrome package distributed by Google, instead of chromium (which is probably what Google wants, really).
The section I put here in bold (the emphasis is mine) is the only course of action you have available to you if you want to use the Google profile sync still - stop using Chromium and instead switch to Google Chrome which does have access to the profile sync API bits at Google, and in turn will do Profile Sync.
If you are unwilling to switch to the full Google Chrome browser, then you are out of luck - there's literally nothing that the world or community at large can do on this.