In WhatsApp, the blue circle around a friend's profile picture indicates that they have posted a new status, such as a photo or video. The absence of a blue circle around another friend's profile picture means that they have not posted any new status updates.
WhatsApp uses these indicators to let you know when someone in your contacts has added a new status, so you can view and interact with it if you wish. If you want to view your friends' statuses, you can do so by tapping on the "Status" tab within WhatsApp. From there, you'll see a list of your friends' status updates, including any photos or videos they have shared.
Keep in mind that WhatsApp's interface and features might change over time, so it's always a good idea to check for the latest updates in the app or on their official website if you want to know more about specific features and indicators.