Forum Discussion
Issue with Sync button missing in Modern Document Library.
So recently the sync button disappeared for sites and document libraries in modern UI. In classic they are still there and the sync works. It seems to be only for publishing sites. Anyone ideas? ...
Orion-Skol If you have MFA enabled for everyone, then external users can lose their sync button.
https://docs.microsoft.com/en-us/onedrive/b2b-sync
"Multi-Factor Authentication from an external organization is not yet supported. Only guest accounts that don't require MFA will sync."