Ok so tried this out and it reminded me why we turned the setting to BOTH.
What we want to have is Auth0’s Universal Login show only our SSO auth buttons (e.g. google) and then if the user associated with that is in multiple orgs, show the org selector.
If we use Identifier First, it appears that we MUST show the email field on login, but per this answer we can’t be on Identifier First if we don’t want the email field.