We deployed the grouped notifications experimental feature on mastodon.online and mastodon.social, and are looking for some initial testers to gather performance information and ensure it works properly.
This feature is only available in the web UI for now (see 2nd screenshot)
There are some known issues (around keyboard navigation) and the API is not yet final.
Please open a Github issue if you find any problem with them, so we can fix it before the 4.3-beta1 release!