I have a Xiaomi Redmi 4X Device with stock Android (no custom OS installation or modifications). I run a Radicale CalDAV server at home and have installed the DAVDroid app (via F-Droid). Inside DAVDroid app, I have set up the connection to my CalDAV server and DAVDroid shows up the calendar, so the connection to the server is fine.
Problems occur when I want to use the calendar with the Calendar app on the phone. In the calendar app, I want (i.e. I have) to choose the CalDAV calendar as a "calendar account", but the DAVDroid account is not showing up in the list of available calendar accounts although it definitely exists.
(I did some other tests using the aCalDAV app from the Google Play Store and the aCalDAV account shows up and is working).
Is there maybe a problem that DAVDroid has because it does not have all the needed permissions? I have no idea how to resolve the issue, so any hints are welcome.