External sharing with B2B integration
It includes external sharing of files, folders, list items, document libraries and sites. The integration also expands the one-time passcode authentication experience to SharePoint sites and lists when sharing with external recipients who don't already have a work, school or a Microsoft account (MSA).
When you announced Secure Links in October 2017, the sharing for folder and files was possible for non Microsoft accounts, e.g. a Gmail or other private, external accounts. I tested and confirmed this behavior with several accounts.
A quote from the previous announcement:
Secure links allow external recipients to access files and folders securely without requiring them to create or maintain a Microsoft account.
I try to find a post where Microsoft describes that this feature was limited to work, school or Microsoft accounts after the rollout? Maybe you can help me to find the post or announcement?