View events in separate windows in Calendar on Mac
You can view the details of several Calendar events at the same time by opening events in separate windows.
Always open events in separate windows
In the Calendar app on your Mac, choose Calendar > Preferences, then click Advanced.
Select “Open events in separate windows.”
Open an event in a separate window
In the Calendar app on your Mac, double-click the event you want to open in a separate window.
Place the pointer over the top edge of the window, then drag the window where you want it.