Hello,
following Situation: I have a Xiaomi Redmi 4X and a CalDav Server on which my calendars live.
With my two former Android Phones there were no Problems, just install the DAVDroid App, input Username and URL, click away the SSL warning (self signed certificate) and they show up in the default calendar app.
Xiaomi on the other hand uses a different Calendar App in their Android Version/Distribution/Abomination and the Accounts just do not show up.
Having described my problem, my question is: Is there a usable Calendar App that does natively do Caldav?