User blog comment:MisterWoodhouse/Social Activity, the 2010 Editor, and Unpausing Migrations/@comment-45689497-20201005163140/@comment-1038387-20201005174319

You should still get notifs for UCP Wall messages, but the UCP wiki has no need for the envelope so you indeed can't see Legacy wall messages. Legacy Wall will be gone, so there's no point in adding it temporarily.