he first thing you must do is log into your Nextcloud account. Go to the Contacts app and, in the bottom left corner, click on the Settings gear icon. Click on the menu button (three horizontal dots) and then, from the drop-down menu, click Copy link.
Now head over to Thunderbird and open the Card Book tab. In this window, right-click the left pane and select New Address Book.
In the first window of the wizard select Remote and click Next. In the second window (Figure C), select CardDAV and then paste the URL from Nextcloud in the URL area. Type your Nextcloud credentials below that and click Validate.
Once the validation succeeds, click Next. In the resulting screen, give the Address Book a name, select a color, and then click Next. In the final screen, click Finish, and you’re done.
If the newly created Address Book doesn’t immediately sync, click the Synchronize button, and you’re good to go.