Org-caldav has basic support for repeating events and todos. In
particular, simple Org timestamp repeaters such as +3d or +1m can
be succesfully sync’d bidirectionally.
However, complex iCalender recurrences, such as "repeat on the 2nd Tuesday of each month until X date", are not supported.
For Org TODOs with both SCHEDULED and DEADLINE timestamps, each of
the timestamps must have the same repeater, otherwise the behavior is
undefined.
Furthermore, the behavior of Org TODOs with a repeating DEADLINE
timestamp, but no SCHEDULED timestamp, has some subtleties; see the
configuration section: Behavior of recurring TODO deadlines without a start time.