Google Contacts is very useful if you want to sync your contacts with your Google account and make sure you never lose them, but so far you have not been able to back up the information stored in the phone's internal storage. On many Android phones, this is where the details are finally saved thanks to the alternative apps included by the OEMs, so Google has now added a feature that will capture these contacts.
Late last year, the Contacts app acquired the ability to move individual contacts from your phone's external storage to your Google account (and vice versa) without performing a full export or import. However, the new feature replaces it, allowing the app to automatically read and sync contacts stored on your device so you don't have to worry about losing them if something happens to your cell phone.
Whether this feature is available to you or not will depend on the phone you have. In Pixels, for example, you can't save contacts to internal storage in the first place; instead, you must save a new entry in one of the accounts you have entered on your mobile device. On the phones of many other original equipment manufacturers, you have the option to save new contacts to your device (via Google Contacts or an alternative manufacturer application) and this is the information that Google will now endorse.
Google's trend for server-side launch means these features may or may not have reached you. At Samsung Galaxy S10 +, the latest version of the Contacts app gives me a new popup in the opening (above) that asks me if I want to sync device contacts with my account. There is also a new settings section called 'Contact sync settings' where you can change it at any time. It's even in pixels, even though they don't allow storage of device contacts.
However, on OnePlus 7T Pro, even with the same version of the Contacts app, it is not yet available. What still exists is the option to move contacts from your Google account to the phone's internal storage (see below).
It makes sense that the new backup and sync settings for device contacts override the previous implementation of OnePlus 7T Pro: if the device contacts are synced with your Google account, moving the contact between the two is excessive. We can assume that the new sync settings will be released to the Contacts app on other phones in time (every time the server side switch is activated).
Please note that this does not affect contacts stored on your SIM card or with other cloud services like Exchange, as they will not automatically sync with your Google account yet.
Having the latest version of Google Contacts (18.104.22.1685716224) gives you the best chance to get this new feature, and you can download it from APK Mirror if it is not already available to you through Play Store. For more information on how to set up a new device sync, see the Google support page on the subject.