On February 7, Microsoft announced the preview of Azure AD cross-tenant access, a new capability to allow users obtain credentials in their home tenant and use these credentials to access resources in other Microsoft 365 organizations. Microsoft Teams Connect (aka shared channels) is likely the first app to use cross-tenant access, with public preview of that feature expected in March 2022.
https://office365itpros.com/2022/02/08/azure-ad-cross-tenant-access/
