Let the user choose where to save a new contact
Use cases
When Contacts is first used with a local address book, and later Google account is added to Online Accounts (which means Google contacts appear in Contacts), the user is not aware that new contacts are still created as local contacts, and that a manual configuration in Preferences is needed to change that.
Desired behavior
Please let the user choose the desired location (local address book, Google address book, etc) when creating a new contact. Individually, for each new contact.
Benefits of the solution
It will be clear to the user where the new contact is saved. There will be no confusion when some users expect their Google address book to be populated when it's in fact not (and Contacts is very silent about this).
Possible drawbacks
I don't see any.