A new visual indication has been added to the Calendar. This indicates when the selected device has been active.  It works as follows.

Upon opening the calendar, you will notice a loading spinner on the bottom right – that indicates that the device history is being fetched from the server.

Shortly after green dots will appear beneath dates for when the device was active.

Additionally, there is some information available in the “How to use the calendar” tooltip

Here’s a short video demonstrating the feature in action: https://www.loom.com/share/11c0a9461feb43a78d6ae703478ce5e4