Have you tried adding/creating the calendar (or maybe firstly the corresponding account) in system settings account manager? (or DAVx5?)
And then to choose it from within the calendar app?
I confirm the same behaviour of my S7 with 1.9.
That’s a bug worth being reported as an issue.
Trying to add a caldav calendar and coming from the calendar app should bring you directly to system settings account manager (which anyways has a davx5-fork already included - no need to bring up davx5 as an extra app…)