How to Co-author Office Documents Protected by Sensitivity Labels

Microsoft has released a preview of co-authoring for protected (encrypted) Office documents using the desktop apps. While it might seem straightforward to enable co-authoring (and the online apps have been able to do this for over a year), making it work for the Office desktop apps requires a complex mix of Office, SharePoint Online, the OneDrive sync client, and sensitivity labels. Once everything lines up, it works beautifully, even if you can’t take a screenshot to prove that it works.

https://practical365.com/blog/co-authoring-protected-office-documents/