There are two methods available for linking users to their Office 365 user account in Foldr, either manually which requires a one time linking process to be completed or automatically. The method of account linking used will affect a users signed in permissions in SharePoint sites and the document libraries available to them via Foldr.
Automatic account linking provides the convenience of automatically presenting the users corresponding OneDrive and any SharePoint sites when they sign into Foldr, however their access level in SharePoint is determined by the service account used to connect. As such, if granular access permissions are set on folders etc, these cannot be respected for each user. Microsoft do not currently allow impersonation for cloud accounts via service accounts in the same way that Google provide with G Suite, and until this functionality / support is provided, this limitation will be in place. More information is available here:
https://developer.microsoft.com/en-us/graph/docs/concepts/permissions_reference
Manual account linking will fully respect an users individual permissions in SharePoint, in the same way as if they were signed into the Office 365 portal directly.