For many sites, just hiding them isn't enough - if you want the website to work properly and not randomly log you out immediately after logging in, then you need to either accept or decline cookies.

Very odd, uBlock Origin for Chrome has "EasyList Cookies Notices", but "AdGuard – Cookie Notices" is missing. The Firefox extension has both lists. The version is the same: uBlock Origin 1.49.2.

Does this have anything to do with Chrome's new extension API nerfing ad blockers?

I'm not sure. I'm in Firefox, but I did have to refresh the sources in the uBO settings and more showed up.