When Azure AD finally moved to the new portal, Microsoft quietly took away the button to add an external user (from another Azure AD or a MS account) directly. Now the only option seems to be to invite users as guests and send them an email link. This also denotes them with a UserType of Guest.
This is prohibitive in a B2C or multi-tenant intranet scenario. We can’t have to email invites around to get people added across directories. Adding users via a B2B spreadsheet import doesn’t seem to get them added as a non Guest either.