[trace] --> PROPFIND /cal.php HTTP/1.1
[trace] <-- HTTP/1.1 401 Unauthorized (154ms)
As you can see, Baïkal doesn’t accept the user credentials. Did you either disable preemptive auth. in DAVdroid or set Baïkal to Basic auth. as described on https://davdroid.bitfire.at/configuration (see the notes for Baïkal)?
The nginx version supports the dav extensions.
There’s no need to enable
ngx_http_dav_module unless you want to use WebDAV file synchronization with your nginx server. All CalDAV/CardDAV stuff is passed to and processed by Baïkal.