Why Google's CardDAV server isn't
https://evertpot.com/google-carddav-issues/, posted 2018 by peter in calendar crapification google opinion sync
The fact that Google advertises their servers as supporting CardDAV is an insult to anyone who does try to be standards compliant.
The Google CardDAV server has similarities to what we call CardDAV. For very simple, controlled stuff, it may be possible to pretend it is.
For anything advanced, avoid it at all cost.