Draft until documentation is updated
Affected version(s):
Symptom
Since the installation of Thunderbird 78 or later the sync of the calendar isn't working anymore.
Root Cause
Because of the merge of the calendar plugin lightning into Thunderbird the user-agent changed from Lightning to Thunderbird. This matters only if you use the UserAgent method to recognize the traffic.
Solution
Have a look at the updated documentation:
https://documentation.open-xchange.com/latest/middleware/miscellaneous/caldav_carddav.html
You can add the RewriteCond for Thunderbird or use one of the other possible methods.
STATUS: documentation fixed