How to identify SSO users in Atlassian Organization?

My organization have both managed and un-managed accounts. How to get all managed accounts in an organization? Is all managed accounts (account have verified domain) is SSO users?
Recently, I’m using bulk get users API to get all users. And I don’t see any field to recognize the sso users.
Also, I see the get users in organization API too. I see the field access_billable returned in the response. Is it SSO user if access_billable === true?

How Atlassian recognize SSO user by email to display the text when user login to Atlassian products?

Thanks all!