How do I create & update CNContacts on macOS?

1. My attempts at creating a new CNContact fail with error message EXC_BAD_ACCESS (code=1, address=... at runtime
2. Attempting to update an existing record appears to change the CNContact record, but the change is not visible in Apple's Contacts app. Code:

Code I have so far:

var status: Bool = false

    store.requestAccess(for: CNEntityType.contacts) { hasPermission, error in
        if error != nil {
            print(error!)
        }
        status = hasPermission
    }

    let newContact = CNMutableContact()

    newContact.givenName = "NBED-given"
    newContact.familyName = "NBED-family"

    let saveRequest = CNSaveRequest()
    saveRequest.add(newContact, toContainerWithIdentifier: store.defaultContainerIdentifier())

    do {
        try store.execute(saveRequest)
    }
    catch {
        print("Error:\t\(error)")
    }

... and ...

guard let contact = contactToAmend.mutableCopy() as? CNMutableContact else { return }
    contact.givenName = "NEW NAME"

    let saveRequest = CNSaveRequest()
    saveRequest.add(contact, toContainerWithIdentifier: store.defaultContainerIdentifier())

    do {
        try store.execute(saveRequest)
        print("Stored ok")
    }
    catch {
        print("Error:\t\(error)")
    }

Looking up this Contact in the Contacts app, I can search for it with the new given name ("NEW NAME"), but the record is then shown with its old (unchanged) name. It's also worth adding that I am seeing a number of messages / warnings in XCode during runtime:

2023-01-06 14:17:45.628226+0000 [api] Attempt to read notes by an unentitled app
2023-01-06 14:17:54.164223+0000 Metal API Validation Enabled
2023-01-06 14:17:54.436906+0000 [api] Attempt to write notes by an unentitled app
CoreData: warning: Unable to load class named 'ContactsPersistence.CNEWSContactFolder' for entity 'ContactFolder'.  Class not found, using default NSManagedObject instead.
CoreData: warning: Unable to load class named 'ContactsPersistence.CNEWSMapping' for entity 'Mapping'.  Class not found, using default NSManagedObject instead.
2023-01-06 14:17:54.771035+0000 [ABCDContact] An ABCDRecord is being saved without having a container assignment. Assigning the contact to <CNCDContainer 0x600000a89980 ab>. Please remember to assign contacts to containers to avoid recurring container lookup and contact re-validation costs.

What am I missing? What am I doing wrong? Thanks for any help you can offer!