Previously, we were working around this SSO limitation by composing the call to /admin/users/sync_sso with another call to /u/{username} endpoint just to clear the name (if the new value for name was empty).
This however seems to also have stopped working at some point in a recent version, possibly because it checks if sso_overrides_name = true before updating the name.
So, as is, when using SSO and sso_overrides_name = true, now it seems to be impossible for the SSO provider to clear the name field on Discourse via the API.
Can you see any workaround this, @sam?