Pinning the entire document library is supported today. Learn more here, https://support.microsoft.com/en-us/office/add-a-sharepoint-page-or-list-to-a-channel-in-teams-131edef1-455f-4c67-a8ce-efa2ebf25f0b.
We currently do not support pinning a specific folder, but we are considering this feature.
An error occurred while saving the commentAnonymous commented
Current SharePoint Document Library Tab only supports adding the root folder of the SharePoint library. Most teams/users need a way to get to specific folders on other SharePoint Sites/Libraries and having a Tab from within Teams will be great way to enable this capability.
This feature is on the backlog. I will update you when we have more details to share.