I don’t know if I can add any helpful information for troubleshooting your
problem, but I can confirm that in my case, Akonadi is working correctly with
CalDav and CardDav running on a Nextcloud server. I am running the current
packages in testing, which will shortly become bookworm. Perhaps you might
consider upgrading, which also gives you the ability to provide feedback on
any bullseye > bookworm transitions.
--
Soren Stoutner
so...@stoutner.com