What do the colored circles near the photo mean?

Colored circles near the user's photo or name indicate their online status.

Green circle - the user is online and is currently on the site or in the app.
Yellow circle - the user was recently online.
Gray circle - the user is offline. Write to them so that they receive a notification.

If there is no circle near the photo, this means that the user has not been online for a long time. But if you write to them or send them a sympathy, they will receive a notification and, perhaps, they will return.