The “last online” status in WhatsApp is intended to give users an understanding of when someone was last active on the app. This information is not available for everyone to see by default because it would be an invasion of privacy for users. In order to protect user privacy, WhatsApp only allows users to see the “last online” status of people who have allowed them to view it. If you have someone in the contacts list that does not have it enabled, you will not be able to see when they were last online.