The Activity feed helps keep you across all of your notifications, it includes;

• Unread - Messages that have not yet been read
• Mentions - When someone mentions you using @yourname 
• Reactions - When someone likes or reacts to something you have posted
• Missed call - Any missed calls
• Voicemail - Missed call where a voicemail was left
• Apps - Notifications from installed apps
• Trending - Posts in channels that are trending (large engagement from other people in that channel)

To search for notifications

1. Select Activity, then select the Filter Icon
   
2. Type in keyword/s to search by. The list will update as you type.
   
3. Tip. You can also narrow down the search by selecting the ellipses ( ... / 3 dots) and selecting a specific notification type.