Nextcloud overview asks for password for sabre/dav and complains about database

These TBSync settings worked for me with Webtop, autodetection did not work.

Here are instructions for Webtop CalDav/CardDav client and server.

For mails there’s IMAP which is a single store for mails but there’s no such thing for contacts and calendars. The apps have their own implementation, saving it to a database.

There’s already a feature request as regards central control of caldav/carddav.

I never tested it, but it seems possible, Nextcloud can be caldav/carddav server and client (via mail app) too.

Same here, name@domain.tld worked for me.