User blog comment:MisterWoodhouse/The first migrations to the Unified Community Platform/@comment-5481613-20201007134955/@comment-24006128-20201007141915

You're talking about two different features.

The one on UCP is called Recent Changes, which was also on the legacy platform, as it is part of MediaWiki's core software.

The one left on legacy, WikiActivity, was a custom feature designed in the Wikia days for showing new users where activity was happening for them to join in on.