After I was struggling the whole day with DAVx5 I found that similar WebDAV account was already available from accounts settings.
Now I’ve successfully established sync with my radicale server the phone syncs every two minutes which is quite excessive.
Is there a setting to reduce the sync-interval somewhere?!
A workaround to arrive to Account Manager options on Nougat:
choose /e/ Address book
or Google Address book
or WebDav Address book,
and finally you get to the missing options of Davx/Account manager to setup all the entries.
Great! That did the trick!
Would never have guessed I had to go over ‘add account’ to reach the settings.
That is why the one DAV-menu item is called ‘Account Manager - Address Book’
Could even remove the leftover DAVx5 account this way.