Azure AD B2B resources The partner uses their own identities and credentials; Azure AD is not required. You don’t need to manage external accounts or passwords. You don’t need to sync accounts or manage account lifecycles. Managing externals: SharePoint Online Azure AD B2B – Custom email invites for users using PowerShell Powershell to invite B2B users: reading “Azure AD B2B resources”

Office 365 – External access

 External access for Office 365 applications: