As you have no earlier reply, I would guess that some CalDAV “connection” is not made.
Not same issue but may be some common ground with a thread like Nextcloud integration via murena.io login in e/OS/ (??).
In a default setup we see:
So you might check
Settings > Accounts > named_murena_a/c> My Account > Settings > Settings additional > tap account_name ID > CALDAV > two lower right icons > (long press to reveal) tap > refresh | sync now