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
I've added a few tabs linking to different SharePoint pages, they all belong in the same Teams SharePoint Online site. On Teams Desktop, none of the pages will load unless I load a tab linking to Home first. And I don't need to load Home of the existing group, even if I load Home from a different group, then the other pages will then load, but if I don't do this, I get nothing, no even an error. This is weird ...
This feature request is working its way through the backlog queue. No new details are available yet.