It looks like this feature has been removed in the transition to New Teams. I really like this feature and will miss having it. See this Microsoft Learn article, for all features that are changing. "Classic Teams: Allow users to follow another user's presence, then notify them of availability. New Teams: Select a user’s avatar or profile photo anywhere in new Teams to quickly get an overview of their online status, next available calendar slot in Outlook, work hours, local time, or work location (remote or office)."