This feature is relatively new and less well tested, so it is recommended to have backups before using it. It has been tested on nextcloud and radicale.
To sync TODO’s between Org and the CalDav server, do:
(setq org-icalendar-include-todo 'all
org-caldav-sync-todo t)
The first instructs the Org exporter to include TODOs; the second tells org-caldav to import icalendar VTODOs as Org TODOs.
Other customizations to consider (see their documentation for more details):
org-caldav-todo-priority to control how priority levels map between
iCalendar and Org.
org-caldav-todo-percent-states to convert between
org-todo-keywords and iCalendar’s percent-complete property.
org-caldav-todo-deadline-schedule-warning-days to auto-create
SCHEDULED timestamps when a DEADLINE is present (this might be useful
for users of the OpenTasks app).
If you find that some Org entries get an extra tag which equals their CATEGORY, this might be caused by the CATEGORY being exported to iCalendar, and then re-imported to Org as a tag. In that case, do
(setq org-icalendar-categories '(local-tags))
to prevent the CATEGORY from being exported to iCalendar. This problem only seems to affect some CalDav servers: in particular, NextCloud is affected, but Radicale does not seem to experience this problem.