Contacts Only Sync With One Service
I've traditionally kept my contacts synced via a Google account but with the recent support for Nextcloud I've switched over to that. The problem is that it seems like contacts synced via Google don't get picked up by Nextcloud. I'm guessing that Google contacts are somehow stored differently, away from where NC can see them?
Even if for some reason the dev team decides that the correct solution is that contacts can only sync with one service at a time there should be an option to export your contacts from Google or another provider into a file and then read them back in so that they can be synced with your new provider.