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 commentTom commented
Currently we can only add lists that are inside a team, which doesn't really work for us. We have lists we work on that are present on other sites (e.g. time tracking).
Adding them as a website works but it's really clunky, it would be great if it was added as a SharePoint list.