Monterey (12.3.1) can't sync with Netxcloud's (23.0.4) CardDAV

Hi, first off it's working on iPhone, Windows, Linux etc. just Monterey somehow can't handle the sync.

Whenever i try to connect, i'll get:

"Unable to verify account name or password."

Using an app-specific password (which works in iPhone e.g.).

Also using advanced config:

Tried for the "principals/users" following stuff:

/remote.php/dav/addressbooks/users/<MY_USER>/contacts/

/remote.php/dav/principals/users/<MY_USER>/

With 443 and SSL ticked.

-> Any idea what else i could try. Been through so many forums/threads and all indicate that macOS can't handle the CardDAV standard really good. If so, how to escalate to Apple?

PS: CalDAV works like a charm.