By default, the number on your app icon (or browser tab) shows unread notifications—so you see how many notifications you haven’t opened yet. If you prefer to see tasks due today on the badge instead, open Profile → Notifications (or Settings), turn on App Icon Badge, and choose Tasks due today. Changes apply only on that device.
Example
New users see unread notification count on the badge. Switch to "Tasks due today" in the same settings section if you’d rather focus on today’s task count at a glance.