I have a couple of questions regarding the full calendar application parent:
Is there any reason why fullcalendar macro parent version remained at 8.4?
Also, I’ve noticed that the contrib mocca calendar, that depends on FullCalendar application, uses XWiki parent version 11.10.4. Should the parent version of mocca calendar be also upgraded before I upgrade the full calendar parent?
Most extensions simply keep the same parent until they need to upgrade. I doubt there is a strong reason to stay on 8.4, by @ClemensRobbenhaar might know more.
At least, the contrib Mocca Calendar will have to upgrade its parent to use the new fullcalendar version if you upgrade fullcalendar parent version.
there is no particular reason for the parent of full calendar, it should be upgraded as needed
mocca calendar depends on full calendar, so mocca calendar application should decide what it does about its dependencies. You don’t need to do anything, as long as mocca calendar depends on the current version of fullcalendar nothing will change for it.